There are provided methods for preparing lithium hydroxide. For example, such methods can comprise submitting an aqueous composition comprising a lithium compound to an electrolysis under conditions suitable for converting at least a portion of said lithium compound into lithium hydroxide. There are also provided methods for preparing lithium sulphate.
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1. A process for preparing lithium hydroxide, said process comprising:
submitting an aqueous composition comprising lithium sulphate to an electrolysis under conditions suitable for converting at least a portion of said lithium sulphate into lithium hydroxide, wherein during said electrolysis, said aqueous composition comprising lithium sulphate has a ph of about 9.5 to about 12.5.
13. A process for preparing lithium hydroxide, said process comprising:
submitting an aqueous composition comprising a lithium compound to an electrolysis under conditions suitable for converting at least a portion of said lithium compound into lithium hydroxide, wherein during said electrolysis, said aqueous composition comprising said lithium compound has a ph of about 9.5 to about 12.5.
19. A process for preparing lithium sulphate, said process comprising:
leaching an acid roasted lithium-containing material with water so as to obtain an aqueous composition comprising li+ and at least one metal ion, wherein the lithium-containing material is a material that has been previously reacted with H2SO4;
reacting said aqueous composition comprising li+ and said at least one metal ion with a base so as to obtain a ph of about 4.5 to about 6.5 and thereby at least partially precipitating said at least one metal ion under the form of at least one hydroxide so as to obtain a precipitate comprising said at least one hydroxide and an aqueous composition comprising li+ and having a reduced content of said at least one metal ion, and separating said aqueous composition from said precipitate; and
contacting said aqueous composition comprising li+ and having a reduced content of said at least one metal ion with an ion-exchange resin so as to at least partially remove at least one metal ion from said composition, thereby obtaining an aqueous composition comprising a lithium sulphate.
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The present disclosure is a continuation of U.S. patent application Ser. No. 15/615,280 filed on Jun. 6, 2017, that is a continuation of U.S. patent application Ser. No. 14/396,109 filed on Oct. 22, 2014, that is a 35 USC 371 national stage entry of PCT/CA2013/000398 filed on Apr. 23, 2013 and that claims priority to U.S. provisional application No. 61/636,869 filed on Apr. 23, 2012 and to U.S. provisional application No. 61/755,151 filed on Jan. 22, 2013. These documents are hereby incorporated by reference in their entirety.
The present disclosure relates to improvements in the field of chemistry applied to the manufacture of lithium hydroxide. For example, such processes are useful for preparing lithium hydroxide from lithium-containing materials. For example, the disclosure also relates to the production of other lithium products such as lithium carbonate and lithium sulphate.
The demand for lithium hydroxide is growing rapidly. The market for lithium hydroxide is expanding and the current world production capacity will likely not meet the expected increase in demand. For example, lithium hydroxide is used for purification of gases and air (as a carbon dioxide absorbent), as a heat transfer medium, as a storage-battery electrolyte, as a catalyst for polymerization, in ceramics, in Portland cement formulations, in manufacturing other lithium compounds and in esterification, especially for lithium stearate.
Lithium batteries have become the battery of choice in several existing and proposed new applications due to their high energy density to weight ratio, as well as their relatively long useful life when compared to other types of batteries. Lithium batteries are used for several applications such as laptop computers, cell phones, medical devices and implants (for example cardiac pacemakers). Lithium batteries are also an interesting option in the development of new automobiles, e.g., hybrid and electric vehicles, which are both environmentally friendly and “green” because of reduced emissions and decreased reliance on hydrocarbon fuels.
High purity can be required for lithium hydroxide that is used, for example, for various battery applications. There is a limited number of lithium hydroxide producers. As a direct result of increased demand for lithium products, battery manufacturers are looking for additional and reliable sources of high quality lithium products, for example lithium hydroxide.
Few methods have been proposed so far for preparing lithium hydroxide. One of them being a method that uses natural brines as a starting material. Battery applications can require very low levels of impurities, notably sodium, calcium and chlorides. The production of lithium hydroxide product with a low impurities content can be difficult unless one or more purification steps are performed. These additional purification steps add to the time and cost of the manufacture of the desired lithium hydroxide product. Natural brines are also associated with high concentrations of magnesium or other metals which can make lithium recovery uneconomical. Thus, the production of lithium hydroxide monohydrate from natural brines can be a difficult task.
There is thus a need for providing an alternative to the existing solutions for preparing lithium hydroxide.
According to one aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium hydroxide, the process comprising:
According to another aspect, there is provided a process for preparing lithium sulphate, the process comprising:
According to another aspect, there is provided a process for preparing lithium sulphate, the process comprising:
In the following drawings, which represent by way of example only, various embodiments of the disclosure:
Further features and advantages will become more readily apparent from the following description of various embodiments as illustrated by way of examples.
The term “suitable” as used herein means that the selection of the particular conditions would depend on the specific manipulation or operation to be performed, but the selection would be well within the skill of a person trained in the art. All processes described herein are to be conducted under conditions sufficient to provide the desired product.
In understanding the scope of the present disclosure, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. The term “consisting” and its derivatives, as used herein, are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The term “consisting essentially of”, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of features, elements, components, groups, integers, and/or steps.
Terms of degree such as “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% or at least ±10% of the modified term if this deviation would not negate the meaning of the word it modifies.
The expression “at least one metal ion”, as used herein refers, for example, to at least one type of ion of at least one metal. For example, the at least one metal ion can be MX+. In this example, MX+ is an ion of the metal M, wherein X+ is a particular form or oxidation state of the metal M. Thus, MX+ is at least one type of ion (oxidation state X+) of at least one metal (M). For example, MY+ can be another type of ion of the metal M, wherein X and Y are different integers.
The expression “is at least substantially maintained” as used herein when referring to a value of a pH or a pH range that is maintained during a process of the disclosure or a portion thereof (for example heating, electrodialysis, electrolysis, etc.) refers to maintaining the value of the pH or the pH range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The expression “is at least substantially maintained” as used herein when referring to a value of a concentration or a concentration range that is maintained during a process of the disclosure or a portion thereof (for example heating, electrodialysis, electrolysis, etc.) refers to maintaining the value of the concentration or the concentration range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The expression “is at least substantially maintained” as used herein when referring to a value of a temperature or a temperature range that is maintained during a process of the disclosure or a portion thereof (for example heating, electrodialysis, electrolysis, etc.) refers to maintaining the value of the temperature or the temperature range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The expression “is at least substantially maintained” as used herein when referring to a value of an oxidation potential or an oxidation potential range that is maintained during a process of the disclosure or a portion thereof (for example heating, electrodialysis, electrolysis, etc.) refers to maintaining the value of the oxidation potential or the oxidation potential range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The expression “is at least substantially maintained” as used herein when referring to a value of an electrical current or an electrical current range that is maintained during a process of the disclosure or a portion thereof (for example electrodialysis, electrolysis, etc.) refers to maintaining the value of the electrical current or the electrical current range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The expression “is at least substantially maintained” as used herein when referring to a value of a voltage or a voltage range that is maintained during a process of the disclosure or a portion thereof (for example electrodialysis, electrolysis, etc.) refers to maintaining the value of the voltage or the voltage range at least 75, 80, 85, 90, 95, 96, 97, 98 or 99% of the time during the process or the portion thereof.
The below presented examples are non-limitative and are used to better exemplify the processes of the present disclosure.
The processes of the present disclosure can be effective for treating various lithium-containing materials. The lithium-containing material can be a lithium-containing ore, a lithium compound, or a recycled industrial lithium-containing entity. For example, the lithium-containing ore can be, for example, α-spodumene, β-spodumene, lepidolite, pegmatite, petalite, eucryptite, amblygonite, hectorite, smectite, clays, or mixtures thereof. The lithium compound can be, for example, LiCl, Li2SO4, LiHCO3, Li2CO3, LiNO3, LiC2H3O2 (lithium acetate), LiF, lithium stearate or lithium citrate. The lithium-containing material can also be a recycled industrial lithium-containing entity such as lithium batteries, other lithium products or derivatives thereof.
A person skilled in the art would appreciate that various reaction parameters, will vary depending on a number of factors, such as the nature of the starting materials, their level of purity, the scale of the reaction as well as all the parameters since they can be dependent from one another, and could adjust the reaction conditions accordingly to optimize yields.
For example, during the electrodialysis or the electrolysis, the pH of the composition comprising lithium sulfate or the lithium compound can be at least substantially maintained at a value of about 9.5 to about 12.5, about 10 to about 12, about 10.5 to about 12.5, about 11 to about 12.5, about 11 to about 12, about 9.8 to about 10.8, about 9.8 to about 10.2, about 10 to about 10.5, or about 10.
For example, during the electrodialysis or the electrolysis, the pH of the composition comprising lithium sulfate or the lithium compound can be at least substantially maintained at a value between 7 and 14.5, 7 and 14, 7 and 10; or 7 and 9.
For example, the pH of the wherein during the electrodialysis or electrolysis, the aqueous composition comprising lithium sulfate or the lithium compound can have a pH between 7 and 14.5, 7 and 14, 7 and 10; or 7 and 9.
For example, the pH of the wherein during the electrodialysis or electrolysis, the aqueous composition comprising lithium sulfate or the lithium compound can have a pH of about 9.5 to about 12.5, about 10 to about 12, about 10.5 to about 12.5, about 11 to about 12, about 9.8 to about 10.8, about 9.8 to about 10.2, about 10 to about 10.5, or about 10.
For example, the electrodialysis or the electrolysis can be carried out in a three-compartment membrane electrolysis cell.
For example, the electrodialysis or the electrolysis can be carried out in a two-compartment membrane electrolysis cell.
For example, the electrodialysis or the electrolysis can be carried out in a three-compartment membrane cell.
For example, the electrodialysis or the electrolysis can be carried out in a two-compartment membrane cell.
For example, the electrolysis can be carried out in a monopolar electrolysis cell. For example, the electrolysis can be carried out in a monopolar three-compartment electrolysis cell.
For example, the electrolysis can be carried out in a bipolar electrolysis cell. For example, the electrolysis can be carried out in a bipolar three-compartment electrolysis cell.
For example, the electrodialysis can be carried out in a bipolar electrodialysis cell. For example, the electrodialysis can be carried out in a bipolar three-compartment electrodialysis cell.
For example, the aqueous composition comprising the lithium sulphate or the lithium compound can be submitted to a monopolar membrane electrolysis process.
For example, the aqueous composition comprising the lithium sulphate or the lithium compound can be submitted to a monopolar three compartment membrane electrolysis process.
For example, the aqueous composition comprising the lithium sulphate or lithium compound can be submitted to a bipolar membrane electrodialysis process.
For example, the aqueous composition comprising the lithium sulphate or lithium compound can be submitted to a bipolar three compartment electrodialysis process.
For example, the electrodialysis or the electrolysis can be carried out in an electrolytic cell in which a cathodic compartment is separated from the central or anodic compartment by a cathodic membrane.
For example, the electrodialysis can be carried out in a bipolar membrane. For example such a membrane is a membrane that splits water molecules (H+ and OH—) and wherein acid and base solution are produced, for example, at low concentration.
For example, the electrolysis can be carried out by using a monopolar membrane. For example, it can be carried out by using an electrolysis stack comprising three compartment cells equipped with monopolar membranes and bipolar electrodes. For example, such electrodes are effective for evolving gaseous hydrogen (H2) at the cathodic electrode and gaseous oxygen (O2) or chlorine gas (Cl2) at the anodic electrode. For example, such electrodes are effective for splitting water molecules.
For example, the membrane can be a perfluorinated membrane or a styrene/divinylbenzene membrane.
For example, the membrane can be a cation exchange membrane, PEEK-reinforced membrane.
For example, the electrodialysis or the electrolysis can be carried out by introducing the aqueous composition comprising the lithium compound (for example LiCl, LiF, Li2SO4, LiHCO3, Li2CO3, LiNO3, LiC2H3O2 (lithium acetate), lithium stearate or lithium citrate) into a central compartment, an aqueous composition comprising lithium hydroxide into a cathodic compartment, and generating an aqueous composition comprising an acid (for example HCl, H2SO4, HNO3 or acetic acid) in an anodic compartment (or acid compartment). The person skilled in the art would understand that, for example, when LiCl is introduced in the central compartment, HCl is generated in the anodic compartment, for example a monopolar membrane electrolysis cell. For example, when LiF is used in the central compartment, HF is generated in the anodic compartment. For example, when Li2SO4 is used in the central compartment, H2SO4 is generated in the anodic compartment. For example, when LiHCO3 is used in the central compartment, H2CO3 is generated in the anodic compartment. For example, when LiNO3 is used in the central compartment, HNO3 is generated in the anodic compartment. For example, when LiC2H3O2 is used in the central compartment, acetic acid is generated in the anodic compartment. For example, when lithium stearate is used in the central compartment, stearic acid is generated in the anodic compartment. For example, when lithium citrate is used in the central compartment, citric acid is generated in the anodic compartment.
For example, the electrodialysis or the electrolysis can be carried out by introducing the lithium sulphate into a central compartment, an aqueous composition comprising lithium hydroxide into a cathodic compartment, and generating an aqueous composition comprising sulphuric acid in an anodic compartment.
For example, an anolyte used during the process can comprise ammonia, ammonium bisulfate, ammonium sulfate and/or NH4OH. For example, an anolyte used during the process can comprise ammonia, ammonium bisulfate, ammonium sulfate and/or NH4OH, thereby generating an ammonium salt.
For example, the process can further comprise adding ammonia and/or NH4OH, for example gaseous or liquid ammonia, for example NH3 and/or NH4OH, in an anolyte compartment, in an acid compartment, in the anolyte, at an anode or adjacently thereof, wherein the anode is used for the process.
For example, the process can further comprise adding ammonia and/or NH4OH, in an anolyte compartment, in an anolyte at an anode or adjacently thereof, thereby generating an ammonium salt, wherein the anode is used for the process.
For example, the process can further comprise adding ammonia and/or NH4OH in an anolyte compartment or in an anolyte used for the process.
For example, the process can further comprise adding ammonia and/or NH4OH in an anolyte used for the process, thereby generating an ammonium salt.
For example, the ammonium salt can be (NH4)2SO4.
For example, concentration of the produced ammonium salt can be about 1 to about 4 M, about 1 to about 3 M, or about 1.5 M to about 2.5 M.
For example, concentration of the ammonium bisulfate present in the anolyte can be at a concentration of about 1 to about 4 M, about 1 to about 3 M, or about 1.5 M to about 3.5 M.
For example, concentration of the ammonium sulfate present in the anolyte can be at a concentration of about 1 to about 4 M, about 1 to about 3 M, or about 1.5 M to about 3.5 M.
For example, pH of the anolyte is maintained at a value of about −0.5 to about 4.0, about −0.5 to about 3.5, about −0.25 to about 1.5 or about −0.25 to about 1.0.
For example, ammonia can be added in a substoichiometric quantity as compared to sulfuric acid produced.
For example, ammonia can be added in a molar ratio ammonia:sulfuric acid comprised between 0.5:1 and 2:1 or between 1:1 and 1.9:1.
For example, the electrodialysis or the electrolysis can be carried out by introducing the aqueous composition comprising the lithium compound (for example LiCl, LiF, Li2SO4, LiHCO3, Li2CO3, LiNO3, LiC2H3O2 (lithium acetate), lithium stearate or lithium citrate) into a central compartment, an aqueous composition comprising lithium hydroxide into a cathodic compartment, and an aqueous composition comprising NH3 into an anodic compartment. For example, when an aqueous composition comprising NH3 is introduced into the anodic compartment, proton-blocking membranes may not be required and membranes which are capable, for example of running at a temperature of about 80° C. and which may, for example, have lower resistance can be used. For example, the aqueous composition comprising the lithium compound can further comprise Na+.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising lithium hydroxide can be at least substantially maintained at a concentration of lithium hydroxide of about 30 to about 90 g/L, about 40 to about 90 g/L, about 35 to about 70 g/L, about 40 to about 66 g/L, about 45 to about 65 g/L, about 48 to about 62 g/L or about 50 to about 60 g/L.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising lithium hydroxide can be at least substantially maintained at a concentration of lithium hydroxide of about 1 to about 5 M, about 2 to about 4 M, about 2.5 to about 3.5 M, about 2.7 to about 3.3 M, about 2.9 to about 3.1 M or about 3 M.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising sulphuric acid can be at least substantially maintained at a concentration of sulphuric acid of about 30 to about 100 g/L, about 40 to about 100 g/L, about 40 to about 100 g/L, about 60 to about 90 g/L, about 20 to about 40 g/L, about 20 to about 50 g/L, about 25 to about 35 g/L, or about 28 to about 32 g/L.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising sulphuric acid can be at least substantially maintained at a concentration of sulphuric acid of about 0.1 to about 5 M, about 0.2 to about 3M, about 0.3 to about 2 M, about 0.3 to about 1.5 M, about 0.4 to about 1.2 M, about 0.5 to about 1 M, or about 0.75 M.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising lithium sulphate can be at least substantially maintained at a concentration of lithium sulphate of about 5 to about 30 g/L, about 5 to about 25 g/L, about 10 to about 20 g/L, or about 13 to about 17 g/L.
For example, during the electrodialysis or the electrolysis, the aqueous composition comprising lithium sulphate can be at least substantially maintained at a concentration of lithium sulphate of about 0.2 to about 3 M, about 0.4 to about 2.5 M, about 0.5 to about 2 M, or about 0.6 to about 1.8 M.
For example, during the electrodialysis or the electrolysis, temperature of the aqueous composition comprising lithium sulphate or lithium compound can be at least substantially maintained at a value of about 20 to about 80° C., about 20 to about 60° C., about 30 to about 40° C., about 50 to about 60° C., or about 46 to about 54° C.
For example, when an aqueous composition comprising NH3 is introduced into the anodic compartment during the electrodialysis or the electrolysis, temperature of the aqueous composition comprising lithium sulphate can be at least substantially maintained at a value of about 20 to about 80° C., about 75 to about 85° C., about 20 to about 60° C., about 30 to about 40° C., about 35 to about 65° C., about 40 to about 60° C., about 35 to about 45° C., about 55 to about 65° C., about 50 to about 60° C. or about 46 to about 54° C.
For example, during the electrodialysis or the electrolysis, electrical current can be at least substantially maintained at a density of about 400 to about 3000 A/m2, about 500 to about 2500 A/m2, about 1000 to about 2000 A/m2 about 400 to about 1200 A/m2, about 400 to about 1000 A/m2, about 300 to about 700 A/m2, about 400 to about 600 A/m2, about 425 to about 575 A/m2, about 450 to about 550 A/m2, or about 475 to about 525 A/m2.
For example, during the electrodialysis or the electrolysis, electrical current can be at least substantially maintained at a density of about 30 to about 250 mA/cm2, 50 to about 250 mA/cm2, about 75 to about 200 mA/cm2 or about 100 to about 175 mA/cm2.
For example, during the electrodialysis or the electrolysis, electrical current can be at least substantially maintained at a constant value.
For example, during the electrodialysis or the electrolysis, voltage can be at least substantially maintained at a constant value.
For example, during the process, voltage can be at least substantially maintained at a constant value that is about 3 to about 10 V or about 4 to about 7 V. For example, the cell voltage can be at least substantially maintained at a value of about 1.0 V to about 8.5 V, about 1.0 V to about 3.0 V, about 2.0 V to about 3.0 V, about 3.0 V to about 8.5 V, about 6.5 V to about 8 V, about 5.5 V to about 6.5 V or about 6 V.
For example, during the electrodialysis or the electrolysis, the overall current efficiency can be about 50% to about 90%, about 60% to about 90%, about 60% to about 85%, about 60% to about 70%, about 60% to about 80%, about 65% to about 85%, about 65% to about 80%, about 65% to about 75%, about 70% to about 85% or about 70% to about 80%.
For example, during the electrodialysis or the electrolysis, the overall LiOH current efficiency can be about 50% to about 90%, about 60% to about 90%, about 60% to about 70%, about 60% to about 80%, about 65% to about 85%, about 65% to about 80%, about 65% to about 75%, about 70% to about 85% or about 70% to about 80%.
For example, during the electrodialysis or the electrolysis, the overall H2SO4 current efficiency can be about 55% to about 95%, 55% to about 90%, about 60% to about 85%, about 65% to about 80%, about 85% to about 95% or about 70% to about 80%.
For example, the aqueous composition comprising Li+ and at least one metal ion can be reacted with the base so as to obtain a pH of about 4.8 to about 6.5, about 5.0 to about 6.2, about 5.2 to about 6.0, about 5.4 to about 5.8 or about 5.6.
For example, the aqueous composition comprising Li+ and at least one metal ion can be reacted with lime.
For example, the at least one metal ion comprised in the aqueous composition that is reacted with the base so as to obtain a pH of about 4.5 to about 6.5 can be chosen from Fe2+, Fe3+ and Al3+.
For example, the at least one metal ion comprised in the aqueous composition that is reacted with the base so as to obtain a pH of about 4.5 to about 6.5 can comprise Fe3+.
For example, the at least one metal ion comprised in the aqueous composition that is reacted with the base so as to obtain a pH of about 4.5 to about 6.5 can comprise Al3+.
For example, the at least one metal ion comprised in the aqueous composition that is reacted with the base so as to obtain a pH of about 4.5 to about 6.5 can comprise Fe3+ and Al3+.
For example, the at least one hydroxide comprised in the precipitate can be chosen from Al(OH)3 and Fe(OH)3.
For example, the precipitate can comprise at least two hydroxides that are Al(OH)3 and Fe(OH)3.
For example, the base used so as to obtain a pH of about 4.5 to about 6.5 can be lime.
For example, lime can be provided as an aqueous composition having a concentration of about 15% by weight to about 25% by weight.
For example, the processes can further comprise maintaining the aqueous composition comprising Li+ and the at least one metal ion that is reacted with a base so as to obtain a pH of about 4.5 to about 6.5 at an oxidative potential of at least about 350 mV.
For example, the aqueous composition can be at least substantially maintained at an oxidative potential of at least about 350 mV by sparging therein a gas comprising O2. For example, the gas can be air. Alternatively, the gas can be O2.
For example, the processes can comprise reacting the aqueous composition comprising Li+ and having the reduced content of the at least one metal ion with the another base so as to obtain a pH of about 9.5 to about 11.5, about 10 to about 11, about 10 to about 10.5, about 9.8 to about 10.2 or about 10.
For example, the base used so as to obtain a pH of about 9.5 to about 11.5 can be NaOH or KOH or LiOH.
For example, the base used so as to obtain a pH of about 9.5 to about 11.5 can be NaOH.
For example, the base and metal carbonate can be a mixture of aqueous NaOH, NaHCO3, LiOH and LiHCO3.
For example, the at least one metal carbonate can be chosen from Na2CO3, NaHCO3, and (NH4)2CO3.
For example, the at least one metal carbonate can be Na2CO3.
For example, the aqueous composition comprising Li+ and having the reduced content of the at least one metal ion can be reacted with the another base over a period of time sufficient for reducing the content of the at least one metal ion in the aqueous composition below a predetermined value. For example, the at least one metal ion can be chosen from Mg2+, Ca2+ and Mn2+. For example, the reaction can be carried out over a period of time sufficient for reducing the content of Ca2+ below about 250 mg/L, about 200 mg/L, about 150 mg/L, or about 100 mg/L. For example, the reaction can be carried out over a period of time sufficient for reducing the content of Mg2+ below about 100 mg/L, about 50 mg/L, about 25 mg/L, about 20 mg/L, about 15 mg/L or about 10 mg/L.
For example, the ion exchange resin can be a cationic resin.
For example, the ion exchange resin can be a cationic resin that is substantially selective for divalent and/or trivalent metal ions.
For example, contacting with the ion exchange resin can allow for reducing a content of Ca2+ of the composition below about 10 mg/L, about 5 mg/L, about 1 mg/L or about 0.5 mg/L.
For example, contacting with the ion exchange resin can allow for reducing total bivalent ion content such as Ca2+, Mg2+ and Mn2+ of the composition below about 10 mg/L, about 5 mg/L, about 1 mg/L or about 0.5 mg/L.
For example, the acid roasted lithium-containing material can be leached with water so as to obtain the aqueous composition comprising Li+ and at least three metal ions chosen from the following metals iron, aluminum, manganese and magnesium.
For example, the acid roasted lithium-containing material can be leached with water so as to obtain the aqueous composition comprising Li+ and at least three metal ions chosen from Al3+, Fe2+, Fe3+, Mg2+, Ca2+, Cr2+, Cr3+, Cr6+, Zn2+ and Mn2+.
For example, the acid roasted lithium-containing material can be leached with water so as to obtain the aqueous composition comprising Li+ and at least four metal ions chosen from Al3+, Fe2+, Fe3+, Mg2+, Ca2+, Cr2+, Cr3+, Cr6+, Zn2+ and Mn2+.
For example, the acid roasted lithium-containing material can be β-spodumene that has been previously reacted with H2SO4.
For example, the acid roasted lithium-containing material can be obtained by using a process as described in CA 504,477, which is hereby incorporated by reference in its entirety.
For example, the acid roasted lithium-containing material can be a α-spodumene, β-spodumene, lepidolite, pegmatite, petalite, amblygonite, hectorite, smectite, clays, or mixtures thereof, that has been previously reacted with H2SO4.
For example, the base-baked lithium-containing material can be β-spodumene that has been previously reacted with Na2CO3 and with CO2, and eventually heated.
In the processes of the present disclosure, the pH can thus be controlled by further adding some base, some acid or by diluting. The ORP can be controlled as previously indicated by sparging air.
For example, when reacting the aqueous composition comprising Li+ and the at least one metal ion with a base so as to obtain a pH of about 4.5 to about 6.5 and thereby at least partially precipitating the at least one metal ion under the form of at least one hydroxide so as to obtain a precipitate, the metal of the at least one metal ion can be Fe, Al, Cr, Zn or mixtures thereof.
For example, when reacting the aqueous composition comprising Li+ and having the reduced content of the at least one metal ion with another base so as to obtain a pH of about 9.5 to about 11.5, and with optionally at least one metal carbonate, thereby at least partially precipitating at least one metal ion, the metal of the at least one metal ion can be Mn, Mg, Ca or mixtures thereof.
For example, when contacting the aqueous composition comprising Li+ and having a reduced content of the at least one metal ion with an ion-exchange resin so as to at least partially remove at least one metal ion, the at least one metal ion can be Mg2+, Ca2+ or a mixture thereof.
As shown in
Acid Roasted β-Spodumene (AR β-spodumene)
Two different blends of the AR β-spodumene were tested. The samples were composed of different ratios of the flotation and dense media separation (DMS) concentrates. The samples were identified as 75/25 and 50/50. The former sample contained about 75% by weight of the flotation concentrate and about 25% by weight of the DMS concentrate. The latter sample contained substantially equal portions by mass of the two concentrates. The assay data of the feed samples is summarized in Table 1. The two samples had very similar analytical profiles. The 75/25 sample had higher levels of Fe, Mn, Mg, Ca and K than the 50/50 sample. Both samples had typical compositions for AR β-spodumene.
TABLE 1
Assay Data of the AR β-Spodumene Samples
Li
Si
Al
Fe
Na
S
Sample
%
75/25 Comp
2.24
25.0
10.5
1.04
0.39
6.09
50/50 Comp
2.29
24.4
10.4
0.96
0.36
6.06
Cr
Zn
Mn
Mg
Ca
K
Sample
g/t
75/25 Comp
167
134
1962
1186
3431
3653
50/50 Comp
163
103
1755
905
2311
3376
Concentrate Leach (CL) and Primary Impurity Removal (PIR)
The objectives of the Concentrate Leach (CL) and the Primary Impurity Removal (PIR) were 1) to dissolve lithium sulphate contained in the AR β-spodumene and 2) to remove the major impurities from the process solution that co-leach with lithium from the feed solids.
A four tank cascade was used for the combined CL and PIR process circuit (see
About 1,200 kg of the 75/25 and about 1,400 kg of the 50/50 AR β-spodumene samples were leached in about 85 hours of operation. The change over from one feed to the other occurred at the 37th hour of operation. Time zero of the operation was when pulp began to overflow from the CL reactor.
In the CL step, water and solids were combined in an agitated tank at a 50:50 weight ratio and mixed for about 30 to about 45 minutes under ambient conditions. Lithium was extracted along with undesirable gangue metals such as, for example, iron, aluminum, silicon, manganese, and magnesium. The obtained slurry (CL slurry) thus comprised a solid composition and an aqueous (liquid) composition containing solubilized Li+ (lithium ions) as well as solubilized ions of the above-mentioned metals. The CL slurry pH and ORP were monitored but not controlled. Alternatively, the pH can eventually be controlled by further adding some base, some acid or by diluting. The ORP can also be controlled as previously indicated by sparging air. The CL slurry flowed by gravity to the PIR Tank 1. The aqueous composition can alternatively be separated from the solid composition before being introduced in the PIR Tank 1 (or before carrying out PIR. In such a case, the aqueous composition (instead of the whole CL slurry as it is the case for the present example) would be inserted into Tank 1.
After 9 hours of operation there was sufficient volume of the Wash 1 fraction (the first displacement wash fraction generated when washing the combined CL and PIR solids residue) to recycle back to the CL. The initial recycle rate of the Wash 1 was set to about 50% of the water addition requirement of the CL. After 37 hours of operation, this amount was increased to make-up 60% of the water addition to the process. This wash stream contained on average about 12 g/L Li (about 95 g/L of Li2SO4).
Primary Impurity Removal (PIR) was carried out, for example, to substantially remove Fe, Al and Si from the aqueous composition while substantially not precipitating any lithium. In this process, the pH of the concentrate leach slurry (comprising the aqueous composition and the solid composition) was elevated to about 5.6 by lime slurry addition to the three PIR tanks. The lime was added as a slurry having a concentration of about 20 wt %. The CL slurry was thus converted into a precipitate and an aqueous composition. The impurities such as Fe, Al and Si were at least substantially precipitated as insoluble metal hydroxides and found in the precipitate while the lithium ions were substantially found in the aqueous composition. The retention time for the PIR circuit was about 45 to about 60 minutes. Air was sparged into the PIR tanks in order to maintain the oxidative potential of the process slurry at or above about 350 mV. At this level, iron present in the ferrous (Fe2+) form would likely oxidize to ferric iron (Fe3+), a form suitable for precipitation at such a pH. Thus, a precipitate comprising, for example, metal hydroxides of Fe, Al and Si was obtained and eventually separated from the aqueous composition comprising lithium ions. In the PIR, the pH can thus be controlled by further adding some base, some acid or by diluting. The ORP can be controlled as previously indicated by sparging air.
The resulting slurry (comprising the aqueous composition and the solid composition (comprising the precipitate)) was filtered on pan filters. The filtrate (aqueous composition comprising lithium ions and having a reduced content of the above mentioned metals (such as Fe, Al and Si)) proceeded to Secondary Impurity Removal (SIR). The PIR filter cake underwent three displacement washes The first wash fraction was collected separately from the second two washes. The first wash stream was recycled to the CL process as a portion of the water feed stream to recover the contained lithium. Wash fractions 2 and 3 were combined and stored as a solution. This solution can be used for lime slurry make-up to recover the lithium units.
The lithium tenors in CL and PIR are presented in
The pH was substantially steady throughout the operation once the throughput was reduced. The ORP of the slurry in PIR tank 3 was substantially steady and above about 350 mV during the operation. The iron tenors for CL and PIR are presented in
Iron and aluminum profiles are presented in
A mass balance for the CL and PIR circuits is shown in Table 2. Lithium extraction and impurity precipitation is calculated based on solids assays. The mass balance shows that overall about 82% of the lithium present in the AR β-spodumene feed proceeded to Secondary Impurity Removal (SIR). Specifically, about 79% lithium extraction was achieved for the 75/25 blend and about 86% for the 50/50 blend. The portions of aluminum and iron that either did not leach or precipitated totaled about 96% and about 99%, respectively.
TABLE 2
Mass Balance of CL and PIR circuits
Metal Content, mg/L or %
Process Streams
Quantity,
Li
Al
Fe
Cr
Zn
Op Hr
kg
% or mg/L
g/t or mg/L
INPUTS
AR B-Spodumene
13.5
485
2.25
106909
9792
173
130
25.5
436
2.19
102675
10072
192
154
37.5
323
2.15
101087
10352
211
177
49.5
407
2.21
104792
11261
212
148
61.5
435
2.28
106909
8883
212
119
73.5
363
2.31
107438
8813
182
88
80.0
205
2.31
107438
8813
182
88
PIR Wash 1
13.5
113
11200
77
11.2
<0.2
5.6
25.5
252
11200
77
11.2
<0.2
5.6
37.5
214
11200
77
11.2
<0.2
5.6
49.5
273
15300
65
4.3
<0.2
5.9
61.5
273
15300
65
4.3
<0.2
5.9
73.5
249
12300
64
3.1
<0.2
3.5
80.0
157
12600
62
1.5
<0.2
3.6
OUTPUTS
PIR3 Solids
13.5
536
0.60
126491
11960
247
133
25.5
277
0.40
121198
11471
229
160
37.5
268
0.58
119611
13219
211
187
49.5
333
0.31
123315
13079
211
164
61.5
294
0.46
126491
11051
210
140
73.5
282
0.48
124374
10771
201
141
80.0
169
0.50
125962
11051
201
141
PIR3 Solution
13.5
600
10700
37.3
60.5
<0.2
5.5
25.5
642
20100
6.95
1.05
<0.2
3.9
37.5
470
16400
1.3
0.8
<0.2
1.7
49.5
515
24550
36.45
3.3
<0.2
5.4
61.5
582
23500
71
3.2
<0.2
4.6
73.5
484
22800
19.5
2.15
<0.2
3.45
80.0
290
25900
65.5
3.4
<0.2
4.8
Process Streams
Density
Metal Units, g
Op Hr
kg/L
% Solids
Li
Al
Fe
Cr
Zn
INPUTS
AR B-Spodumene
13.5
10912
51847
4749
84
63
25.5
9555
44797
4394
84
67
37.5
6938
32621
3340
68
57
49.5
8995
42653
4583
86
60
61.5
9907
46455
3860
92
52
73.5
8397
39053
3203
66
32
80.0
4732
22007
1805
37
18
PIR Wash 1
13.5
1.06
1195
8
1
0
1
25.5
1.07
2631
18
3
0
1
37.5
1.06
2262
15
2
0
1
49.5
1.10
3800
16
1
0
1
61.5
1.12
3748
16
1
0
1
73.5
1.09
2821
15
1
0
1
80.0
1.08
1829
9
0
0
1
OUTPUTS
PIR3 Solids
13.5
47.2
3218
67836
6414
132
71
25.5
30.1
1107
33534
3174
63
44
37.5
36.3
1556
32094
3547
57
50
49.5
39.3
1032
41042
4353
70
54
61.5
33.6
1354
37238
3253
62
41
73.5
36.8
1353
35070
3037
57
40
80.0
36.8
844
21268
1866
34
24
PIR3 Solution
13.5
1.07
5995
21
34
0
3
25.5
1.12
11477
4
1
0
2
37.5
1.11
6970
1
0
0
1
49.5
1.15
10953
16
1
0
2
61.5
1.15
11926
36
2
0
2
73.5
1.15
9580
8
1
0
1
80.0
1.16
6464
16
1
0
1
Units IN
13.5
12107
51855
4750
84
64
25.5
12186
44815
4397
84
68
37.5
9200
32636
3343
68
58
49.5
12795
42669
4585
86
62
61.5
13655
46471
3861
92
53
73.5
11218
39068
3204
66
33
80.0
6560
22017
1805
37
19
TOTAL
77722
279532
25945
517
356
Units OUT
13.5
9212
67857
6448
132
74
25.5
12584
33538
3174
63
46
37.5
8527
32095
3547
57
51
49.5
11985
41058
4355
70
57
61.5
13281
37274
3255
62
44
73.5
10934
35078
3038
57
41
80.0
7308
21284
1867
34
25
TOTAL
73830
268184
25684
475
338
Extraction
13.5
71
25.5
88
37.5
78
49.5
89
61.5
86
73.5
84
80.0
82
TOTAL
82
Precipitation
13.5
131
135
158
113
25.5
75
72
76
66
37.5
98
106
83
88
49.5
96
95
81
90
61.5
80
84
67
80
73.5
90
95
86
124
80.0
97
103
91
132
TOTAL
96
99
92
93
Accountability, OUT/IN %
76
131
136
158
117
103
75
72
76
68
93
98
106
83
87
94
96
95
81
92
97
80
84
67
82
97
90
95
86
126
111
97
103
91
135
TOTAL
95
96
99
92
95
*Averages if shown in Italics
Secondary Impurity Removal
Secondary Impurity Removal (SIR) was performed on the PIR filtrate (aqueous composition comprising lithium ions and having a reduced content of the above mentioned metals (such as Fe, Al and Si)) to substantially precipitate and remove Ca, Mg and Mn impurities therefrom. Feed addition to the SIR circuit started at operating hour 6 (six hours after overflow from the CL tank). There are four process tanks arranged in a cascade (see
In the first two agitated tanks, the pH was increased to about 10 using about 2 M sodium hydroxide (NaOH) (another base). Following this pH adjustment, an excess of sodium carbonate (Na2CO3) based on levels of targeted impurities in the feed was added to the third tank to convert the remaining divalent impurities to insoluble carbonates. The slurry from the third tank was pumped to a clarifier. Underflow solids were removed and recovered by filtration while the overflow solution was collected in an about 1000 L tote.
Averaged impurity tenors of solutions from the Concentrate Leach stage through to the final tank of Secondary Impurity Removal are shown in Table 3 and
TABLE 3
Profile of Selected Impurities
Li
Al
Fe
Cr
Zn
Mn
Mg
Ca
Stream
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
CL
23880
1737
985
5.9
9.1
178
109
468
PIR1
21290
34
9
0.0
4.3
174
153
435
PIR2
21240
28
8
0.0
4.0
173
175
433
PIR3
21140
30
8
0.0
4.2
174
179
434
SIR1
20093
1
0
0.0
0.0
2
43
426
SIR2
22500
0
0
0.0
0.0
1
19
352
SIR3
19050
1
0
0.0
0.0
1
16
322
SIR4
22400
0
0
0.0
0.0
1
14
241
Impurities introduced in the leach stage included iron, aluminum, chromium, zinc, magnesium, manganese and calcium. Substantially all of the chromium and over about 98% of the iron and aluminum substantially precipitated in the first PIR tank (PIR1). Minimal precipitation occurred in the next two tanks of PIR (PIR2 and PIR3). By the first tank of SIR (SIR1), the only impurities substantially remaining in solution were magnesium and calcium. All other elements were less than about 1 mg/L. Although most of the precipitation occurred in SIR1, the extra retention time of SIR2 dropped the magnesium tenor from about 40 to about 20 mg/L. From SIR2 through SIR4, magnesium and calcium tenors showed a steady decline with more retention time. Impurity levels for SIR4 averaged to about 1 mg/L Mn, about 14 mg/L Mg and about 241 mg/L Ca during the pilot plant run. However, levels as low as about 200 mg/L Ca and about 2 mg/L Mg were attained by the optimization of key parameters.
pH and ORP were monitored throughout the operation. pH was only controlled in the first two tanks. Initially, the selected pH for SIR2 was about 10. At operating hour 30, the pH in SIR2 was increased to about 10.5. With the exception of a 2 hour period at hour 50, where the pH in SIR2 dropped to about 10, pH remained at about 10.5 for the remainder of the run. The average pH values achieved over the two periods were about 10.1 and about 10.5 and the resulting sodium hydroxide consumptions were about 0.022 and about 0.024 kg sodium hydroxide per hour, respectively. The overall sodium hydroxide consumption was about 10 kilograms of sodium hydroxide solution per about 1000 kg of lithium carbonate equivalent (LCE).
The impurity tenors of SIR2 solutions are plotted over time in
Calcium and magnesium tenors in solutions leaving SIR4 are plotted in
Product from the SIR circuit was assayed every about 4 hours as it left the final tank (SIR4) (see
TABLE 4
Effect of Aging on SIR Product
Mg
Ca
Stream
mg/L
mg/L
SIR4 Product
17
286
IX Feed Tote
15
140
A mass balance for the SIR circuit is shown in Table 5. The mass balance shows that overall about 92% of the magnesium and all of the manganese reported to the solids. The distribution of lithium to the solids is about 0.9% for an overall SIR lithium recovery of about 99.1%.
TABLE 5
Mass Balance of SIR circuit
Metal Content, mg/L or %
Process Streams
Quantity,
Mn
Mg
Ca
Op Hr
kg
g/t or mg/L
INPUTS
SIR Feed
13.5
600
72
69
438
25.5
642
109
111
463
37.5
470
146
209
459
49.5
515
199
216
451
61.5
582
227
181
415
73.5
484
203
154
441
80.0
290
195
150
443
OUTPUTS
SIR Solids
Solids Pail 1
3.17
64700
63600
86300
Solids Pail 2
4.03
68000
54700
85200
SIR4 Solution
13.5
176
0.7
18
309
25.5
383
1.2
21
358
37.5
426
1.6
48
370
49.5
395
0.1
20
325
61.5
208
0.2
7.6
191
73.5
214
0.2
1.4
220
80.0
206
0.4
1.5
225
SIR Lithium Recovery
SIR solids, kg Li
0.3
SIR total out, kg Li
36.3
Lithium Recovery, %
99.1
Process Streams
Density
Metal Units, g
Op Hr
kg/L
Mn
Mg
Ca
INPUTS
SIR Feed
13.5
1.08
40
38
242
25.5
1.03
68
69
288
37.5
1.12
62
88
193
49.5
1.14
90
97
203
61.5
1.10
121
96
220
73.5
1.20
81
62
177
80.0
1.17
48
37
109
OUTPUTS
SIR Solids
Solids Pail 1
205
201
273
Solids Pail 2
274
221
343
SIR4 Solution
13.5
1.05
0
3
52
25.5
1.09
0
7
126
37.5
1.11
1
18
143
49.5
1.15
0
7
112
61.5
1.15
0
1
35
73.5
1.20
0
0
39
80.0
1.21
0
0
38
Precipitation =
13.5
100
92
79
(1 − SIR4 solution/SIR Feed) *
25.5
99
89
56
100
37.5
99
79
26
49.5
100
93
45
61.5
100
99
84
73.5
100
100
78
80.0
100
99
65
TOTAL
100
92
62
Accountability, OUT/IN %
94
94
81
Distribution to Solids
100
92
53
Ion Exchange
The SIR product is processed through an ion-exchange (IX) circuit to further reduce the Ca and Mg tenors prior to lithium product production. The IX circuit comprises three columns packed with Purolite™ S950, a cationic resin that can be used in the sodium form that is selective towards divalent and trivalent metal ions. Purolite™ S950 comprises an aminophosphonic resin supported on a macroporous cross-linked polymer. It can be used for the removal of heavy metal cations. At high pH it can be active in the removal of Group 2 metal cations (Mg, Ca and Ba) and Cd, Ni and Co. At high pH divalent metal cations are preferentially absorbed over monovalent metal cations (e.g. Li, Na, K). Any ion exchange resin that would be suitable for substantially selectively removing divalent metal cations such as Ca2+ and Mg2+ and/or trivalent metal cations could be alternatively used in the present disclosure. Alternatively, more than one type of resin can be used to selectively remove the various metal cations. Thus, different ion exchange resins can be used for different metal cations.
The operating philosophy used for the IX circuit was a Lead-Lag Regeneration process (see
The parameters for the IX operation are summarized in Table 6. These parameters were based on the laboratory tests results and the Lead-Lag column configuration was designed to process 75 bed volumes (BV) of feed solution before the Ca and Mg tenors in the Lag effluent exceeded established upper limit that was about 10 mg/L that was established for each cation. After processing 75 BV's of feed solution the combined absorption capacity of the resin in the Lead and Lag columns would not be sufficient to produce a final effluent with the Ca and Mg tenors each below about 10 mg/L. At this point the loading cycle is complete. The Lead column is promoted to the Regeneration stage. The Lag column takes the Lead position. The Regenerated column becomes the Lag column.
The Regeneration stage involved washing the Lead column with reverse osmosis (RO) water to flush out the Li rich solution within the column. This solution is passed to the Lag column. The Feed Wash stage is followed by Acid Strip using about 2 M HCl. This removes the absorbed Ca, Mg, Li and other metal cations from the resin. The resin is now in the acid form. An Acid Wash stage follows to rinse the remaining HCl(aq) from the column. The resin is then converted to the Na form by passing about 2 M NaOH through the column (Regeneration Stage). The final step involves washing the excess NaOH from the column using reverse osmosis (RO) water. The resin is now regenerated and ready to be promoted to the Lag position for the next Loading cycle. The effluent from the Acid Strip cycle was collected separately. The effluents from the Acid Wash, Regeneration and Regeneration Wash cycles were all captured in the same drum.
The Acid Strip stage produces a solution that contains Li, Ca, and Mg. The data indicated that Li elutes from the column first followed by Ca and Mg. It can be possible to separately capture the Li fraction and as a result produce a lithium chloride solution.
TABLE 6
IX Pilot Operation Parameters
Bed Volume
Rate,
IX Stage
Solution
(BV)
BV/h
Loading
IX Feed
75
5
Feed Wash
RO Water
1.5
5
Acid Strip
2M HCl
3
5
Acid Wash
RO Water
5
5
Regeneration
2M NaOH
3
5
Regeneration Wash
RO Water
3
5
1 BV = 10 L
A total of about 2154 L of SIR Product solution was processed through the IX circuit in four cycles. The average Li, Ca, and Mg tenors of the feed solutions for each cycle are summarized in Table 7.
TABLE 7
IX - Average Feed Solution Li, Ca and Mg Tenors
IX
Average Feed Solution Tenor, mg/L
Cycle
Li
Ca
Mg
C1
16480
176
28.2
C2
17600
140
12.9
C3 & C4
21940
78.7
3.6
A cycle was initially designed to operate the Loading stage for 75 BV's. The average loading flow rate was about 832 mL/min (about 49.9 L/h). Cycle 1 was the only cycle where 75 BVs of feed solution was passed through the Lead-Lag columns.
The Ca Loading curve for Cycle 1, where the Ca tenor of the effluents from the Lead and Lag columns are plotted against cumulative bed volume processed, is presented in
A similar loading profile for Mg for Cycle 1 is presented in
Cycles 2 and 3 had to be stopped before 75 BV's of feed solution could be processed through the columns. The Ca tenors of the Lag effluent for each IX cycle are plotted against cumulative BV in
The balance of the Cycle 3 feed solution was processed over about 36.4 BV's in Cycle 4. The Ca breakthrough points for the Lead and Lag columns for Cycle 4 occurred at <about 7.5 and about 7.5 BV, respectively. Extrapolation of the Cycle 4 Lag effluent Ca tenor data indicated that the product solution would have a Ca tenor >about 10 mg/L after 60 BV's.
The Mg tenors of the Lag effluent for each IX cycle are plotted against cumulative BV in
The average Li tenors of the Lead effluent for each IX cycle are plotted against cumulative BV in
The Li, Ca and Mg tenors in the Acid Strip effluents of Cycle 1 and 2 are plotted against cumulative BV in
Reagent consumptions are reported relative to the LCE produced on a kg per about 1000 kg basis. The lithium sulphate stream produced from Ion Exchange contained about 39.1 kg of Li (this includes 100% of the lithium units in a PIR PLS sample that did not undergo SIR and IX). The equivalent mass of lithium carbonate that could be produced given no losses in downstream processes would equal about 187.7 kg.
The IX circuit produced about 2006 L of product solution. The assay data of the IX Product solutions are summarized in Table 8. The Li tenor ranged from about 15.7 to about 21.9 g/L. The ranges of the Ca and Mg tenors were about 2.4 to about 5.7 mg/L and <about 0.07 to about 0.2 mg/L, respectively. Other constituents of note were Na and K at about 3.5 g/L and about 0.1 g/L on average, respectively. The elements that assayed below the detection limits of the analytical technique are also listed in Table 8.
TABLE 8
IX Product Solution Assays
IX
Solution Tenor, mg/L
Product
Li
SO4
Cl
Na
K
Ca
Sr
Mg
Ba
Carboy
15700
120000
5
3980
107
3.8
0.61
0.2
0.03
1
Carboy
16700
120000
4
1990
105
5.7
0.9
0.18
0.043
2
Carboy
21900
160000
5
4470
117
2.4
0.74
<0.07
0.05
3
Elements Assaying below Detection (Detection Limits provided in mg/L)
Ag
Al
As
Be
Bi
Cd
Co
Cr
Cu
Fe
<0.5
<0.8
<3
<0.002
<1
<0.3
<0.3
<0.2
<0.1
<0.2
Mn
Mo
Ni
P
Pb
Sb
Se
Sn
Ti
Ti
<0.04
<0.6
<1
<5
<2
<1
<3
<2
<0.1
<3
U
V
W
Y
Zn
<1
<0.07
<2
<0.02
<0.7
The mass balance for the IX circuit is provided in Table 9. Good accountability for Li was obtained. About 2.7% of the Li was lost in the Strip/Regeneration process solution. The process removed about 97.6% of the Ca and about 99.0% of the Mg contained in the feed solutions.
The IX circuit met the process objectives by reducing the Ca and Mg tenors in the product solution to below about 10 mg/L for each metal cation. Further, a high quality lithium sulphate solution was produced.
TABLE 9
IX Mass Balance
Assays, mg/L or %
Process Stream
Kg or L
Li
Ca
Mg
SIR Feed C1
750
16480
176
28.2
SIR Feed C2
682
17600
140
12.9
SIR Feed C3
359
21940
78.7
3.6
SIR Feed C4
364
21940
78.7
3.6
IX Product Carboy 1
914
15700
3.8
0.2
IX Product Carboy 2
478
16700
5.7
0.18
IX Product Carboy 3
614
21900
2.4
<0.07
IX Regen Reject Drum 1
202
16.9
35.5
2.47
IX Regen Reject Drum 2
208
12.2
16.7
<0.07
IX Strip - Solids
0.8
0.002
26.5
0.0004
IX Strip - Solution
111
8760
718
229
Elemental Masses IN, kg
SIR Feed C1
12.36
0.13
0.02
SIR Feed C2
11.99
0.10
0.01
SIR Feed C3
7.87
0.03
0.00
SIR Feed C4
7.99
0.03
0.00
Total IN, kg
40.2
0.28
0.03
Elemental Masses OUT, kg
IX Product Carboy 1
14.35
0.00
0.00
IX Product Carboy 2
7.99
0.00
0.00
IX Product Carboy 3
13.45
0.00
0
IX Regen Reject Drum 1
0.00
0.01
0.00
IX Regen Reject Drum 2
0.00
0.00
0
IX Strip - Solids
0.00
0.22
0.00
IX Strip - Solution
0.97
0.08
0.03
Total OUT, kg
36.8
0.32
0.03
Distribution, %
Product
97.3
2.4
1.0
Tails
2.7
97.6
99.0
Distribution Total
100.0
100.0
100.0
OUT/IN, %
91.4
112.4
80.3
Li Loss, %
2.7
M Removed, %
97.6
99.0
Examination of the semi-quantitative x-ray diffraction (SQ-XRD) data of composite samples of the CL/PIR residues showed that each sample contains both α- and β-spodumene. The SQ-XRD data for the CL/PIR residues generated from each of the two feed samples (75/25 and 50/50) are summarized in Table 10. The presence of α-spodumene indicates that the phase transition step that was conducted by a third party vendor (acid roast of α-spodumene) was not 100% efficient. Any Li present in this form would thus not be chemically available to the hydrometallurgical process. It should be noted that the efficiency of the phase transition step (conversion from α-spodumene to β-spodumene) is not 100% and therefore a percentage of the contained Li in the feed to the Hydrometallurgical process is as α-spodumene.
TABLE 10
SQ-XRD Data of the two CL/PIR Residue Types
75/25 CL/PIR
50/50 CL/PIR
Chemical
Residue Drum
Residue Drum
Composition
1-5, wt %
7-14, wt %
H(AlSi2)O6
60.6
67.3
Spodumene beta
12.0
9.4
SiO2
11.6
7.5
NaAlSi3O8
3.6
3.8
CaSO4•(H2O)
2.7
4.4
KAlSi3O8
1.6
3.6
LiAlSi2O6
2.2
2.5
Ca(SO4)(H2O)0.5
2.5
—
αFeO•OH
1.9
—
Fe3O4
—
1.6
CaSO4•2H2O
1.1
—
gamma-Mn3O4
0.3
—
100.1
100.1
Li Bearing Mineral
Relative Distribution of Li, %
Spodumene beta
94.9
92.7
LiAlSi2O5
5.1
7.3
The Li units that are in the CL/PIR residues as β-spodumene were never available to the process and as a result provide a false low Li recovery value.
An adjusted Li recovery was calculated that did not consider the Li units tied up as β-spodumene in the CL/PIR residue. The data for this calculation are summarized in Table 11. The total Li in all of the out process streams was about 63.2 kg. This included about 11.7 kg of Li in the CL/PIR residue that was present as β-spodumene. The adjusted total Li out value thus becomes about 51.6 kg. The total recoverable Li by the overall process was about 46.9 kg. The adjusted total Li recovery is then calculated to be about 95.8%.
TABLE 11
Adjusted Total Li Recovery
Li Mass, g
Total Li OUT based on Assays
60615
Total Li Recovered
46884
Total Li in CL/PIR Residue as β-Spodumene
11655
Total Li OUT minus Li as β-Spodumene
48960
Adjusted Total Li Recovery, %
95.8
A high grade lithium sulphate solution was thus produced. In accordance with
Electrolysis: Conversion of Li2SO4 into LiOH
The electrolysis was conducted using an electrolysis method in a monopolar three-compartment membrane electrolysis (ME) cell. The central compartment of the ME cell was separated from the cathodic compartment by a cationic membrane and from the anodic compartment by an anionic membrane. The cathodes comprised stainless steel (316) and the anode comprised a Ti mixed metal oxide (MMO) layer. The basic schematic of the ME cell is provided in
Under the influence of an electric field, lithium ions from the central compartment were transported through the cationic membrane into the cathodic compartment. In parallel the sulphate ions move through the anionic membrane into the anodic compartment. Meanwhile, hydroxyl ions are produced on the cathode and hence lithium hydroxide is formed in the catholyte. The anodic reaction generated protons resulting in the production of sulphuric acid as the anolyte. As a result the lithium concentration increases in the catholyte and drops in the central compartment during membrane electrolysis. During operation the Li tenor in the central compartment was maintained by the controlled addition of a concentrated lithium sulphate solution.
The cathodic and anodic compartments are fed with deionized water in order to keep the lithium hydroxide and sulphuric acid concentrations at predetermined levels.
The synthesis of lithium hydroxide was conducted using a stacked ME cell consisting of two three-compartment cells. The main components of the cell were fabricated with high density polypropylene (HDP). The cathodes comprised 316 stainless steel and were about 100 cm×about 50 cm. The anode was coated with titanium mixed metal oxide (MMO) and was about 100 cm×about 50 cm. The anode was purchased from De Nora Tech (part number: DNT-DX-09-118 Electrowinning Anodes sheet, coating code DN-475E both sides).
The stack design of the ME cell allowed for essentially two ME cells that operated in parallel. Further, the stacked configuration allowed for the anode to be shared by the two cells. Each cell comprises a cathodic compartment equipped with a cathode, a central compartment and an anodic compartment with the shared electrode. The central compartment of the cell was separated from cathodic compartment by a cationic membrane Lanxess Ionac™-MC-3470 and from the anodic compartment by an anionic membrane Lanxess Ionac™-MA-7500. Effective working area of each membrane was about 0.84 m2. The void space within each compartment was filled with polypropylene mesh to aid in dispersing the solution flow. The process flow diagram of the ME circuit is provided in
The electricity to the ME cell was supplied by a direct current rectifier unit, type SR DDS-5C024-02 manufactured by Hanson. The rectifier had both an amp meter and a volt meter that were used for monitoring the voltage and current applied to the cell. The rectifier was set on current control mode.
The lithium sulphate solution produced in the previous sections was used as a lithium source for the ME pilot plant (electrolysisis). The composition of the feed solution is provided in Table 12.
TABLE 12
Composition of Feed Solution
Sample
Tenor of solution components, mg/L
ID
Li
Na
K
Ca
Mg
Fe
Zn
IX
15700
3980
107
3.8
0.2
<0.2
<0.7
Product
Ag
Al
As
Ba
Be
Bi
Cd
Carboy 1
<0.5
<0.8
<3
0.03
<0.002
<1
<0.3
Co
Cr
Cu
Mn
Mo
Ni
P
mg/L
<0.3
<0.2
<0.1
<0.04
<0.6
<1
<5
Pb
Sb
Se
Sn
Sr
Ti
Tl
<2
<1
<3
<2
0.61
<0.1
<3
U
V
W
Y
SO4
Cl
<1
<0.07
<2
<0.02
120000
5
The ME cell was pre-filled prior to the start of the pilot plant. The central compartment of the cell was charged with an aqueous composition comprising lithium sulphate Feed solution that had been diluted down to about 2 g/L Li with RO water (thus about 15.8 g/L of Li2SO4). The cathodic compartment was filled up with an aqueous composition comprising lithium hydroxide. About sixty litres of an aqueous composition comprising sulphuric acid (about 30 g/L) was prepared from reagent acid and used to fill the anodic compartment. The composition of the starting material compositions were thus as follows (see Table 13).
TABLE 13
Compositions of Starting Material Compositions
Tenor of solution components, mg/L
Sample ID
Li
Na
K
Ca
Mg
Fe
Zn
Spent-Init
1300
452
14
<0.9
<0.07
<0.2
<0.7
Ca-Init
3100
740
30
<0.9
<0.2
<0.07
<0.7
An-Init
0.07
<2
<1
<0.9
<0.07
<0.2
<0.7
Ag
Al
As
Ba
Be
Bi
Cd
Spent-Init
<0.5
<0.8
<3
<0.007
<0.002
<1
<0.3
Ca-Init
<0.5
<0.8
<3
<0.007
<0.002
<1
<0.3
An-Init
<0.5
<0.8
<3
<0.007
<0.002
<1
<0.3
Co
Cr
Cu
Mn
Mo
Ni
P
Spent-Init
<0.3
<0.2
<0.1
<0.04
<0.6
<1
<5
Ca-Init
<0.3
<0.2
<0.1
<0.04
<0.6
<1
<5
An-Init
<0.3
<0.2
<0.1
<0.04
<0.6
<1
<5
Pb
Sb
Se
Sn
Sr
Ti
Tl
Spent-Init
<2
<1
<3
<2
0.077
<0.02
<3
Ca-Init
<2
<1
<3
<2
0.049
<0.02
<3
An-Init
<2
<1
<3
<2
<0.002
<0.02
<3
U
V
W
Y
SO4
Cl
Spent-Init
<1
<0.2
<2
<0.02
13000
<1
Ca-Init
<1
<0.2
<2
<0.02
An-Init
<1
<0.2
<2
<0.02
24000
<1
The central compartment of the cell was fed with the fresh aqueous composition comprising lithium sulphate (Feed). The feed flow rate was controlled to maintain about 2 g/L of Li in the central compartment (about 15.8 g/L of Li2SO4). The pH of the aqueous composition comprising lithium sulphate in the central compartment was maintained at a value of about 10 to about 12.
The spent electrolyte from central compartment was bled to the spent bleed tank. The bleed was taken from recirculation tubing before reaching reservoir to ensure a low lithium tenor in the spent electrolyte. The bleed flow rate was controlled to maintain a constant level in the reservoir tank. The anolyte had both a bleed flow from anolyte reservoir and a dilution water flow to the reservoir. The bleed flow rate was controlled to maintain level in the anolyte reservoir by having the bleed tubing at a fixed level in the tank and ensuring the pump was set higher than the dilution water flow rate. The dilution water flow rate was controlled to maintain a concentration of about 30 g/L concerning the aqueous composition comprising sulphuric acid (in the anodic cell (as monitored by free acid titrations)). The catholyte also had both a bleed flow and a dilution water flow to the reservoir. The bleed flow rate for the catholyte was controlled to maintain the level in the reservoir. The bleed was taken from the recirculation tubing before reaching the reservoir to ensure a high Li tenor and no contamination. Dilution water for the catholyte was added to maintain lithium tenor at about 15 g/L (about 51.8 g/L in terms of LiOH) in the catholyte product (aqueous composition comprising LiOH). These flows are illustrated in
Grab samples from the central compartment (the spent solution) were taken every about 4 hours, profile samples were taken every about 6 hours and composite samples were taken every about 12 hours of the anolyte and every about 24 hours for the spent and catholyte. Titrations for lithium hydroxide in the catholyte and free acid titrations for the anolyte were done once an hour.
The ME pilot plant ran in two 5 day sections: Week 1 and Week 2. Each section operated continuously for the five days. Hourly readings were taken to monitor current, voltage, temperature, the flow rates, and product and feed weights. All of the readings were recorded in an Operation Log sheet. At start-up a current of about 400 A was applied to the cell. The recirculation flow rate was set at about 3 L/min and the temperature set points on the cooling water for the circulation tanks was set to about 40° C. During the operation of the pilot plant several changes were made to operating conditions in order to determine the effect the changes would have on production. The first change involved increasing the amperage from about 400 A to about 440 A, to see if it would be possible to increase the feed flow rate without decreasing the product Li tenor. Next the recirculation speed was increased from about 3 to about 6 L/min, to see if this would improve the efficiency of the cell. Another test carried out was to operate on voltage control rather than amperage control, by trying to achieve and maintain about 10 to about 12 V. Finally, the temperature set point on the cooling water for the recirculation tanks was changed to about 50° C. and about 35° C. Membrane electrolysis operation conditions are summarized in Tables 14 and 15.
TABLE 14
ME Pilot Plant Operation Conditions. Week One
Electrolysis
Current
Time
Current
time
quantity
Power
Circ. Rate
Temp.
From
To
A
h
Ah
Wh
L/min
° C.
Day 1
12-11 23:47
12-11 23:59
400
0.2
85
710
3
40
12-05 10:43
12-05 23:59
400
13.3
5287
44837
3
40
12-06 0:00
12-06 6:00
400
6.0
2398
19040
3
40
Total
19.5
7770
64586
Day 2
12-06 6:01
12-06 14:28
400
8.4
3373
31638
3
40
12-06 14:29
12-06 23:59
440
9.5
4164
43448
3
40
12-07 0:00
12-07 5:59
440
6.0
2619
28855
3
40
Total
23.9
10156
103941
Day 3
12-07 6:00
12-07 10:37
440
4.6
2026
24327
3
40
Run 440 A
20.1
8809
96629
12-07 11:40
12-07 23:59
400
12.3
4915
51481
3
40
12-08 0:00
12-08 5:59
400
6.0
2390
27229
3
40
Total
22.9
9332
103037
Day 4
12-08 6:00
12-08 11:59
400
6.0
2392
31380
3
40
12-08 12:00
12-08 19:25
400
7.4
2959
27988
6
40
12-08 19:54
12-08 21:08
400
1.2
490
4274
6
40
12-08 21:16
12-08 23:59
400
2.6
1029
9107
6
40
12-09 0:00
12-09 5:54
400
5.9
2357
21190
6
40
Total
23.1
9227
93939
Day 5
12-09 5:55
12-09 11:59
400
6.1
2423
22159
6
40
Run 6 L/min
23.2
9259
84717
12-09 12:00
12-09 15:29
400
3.5
1394
17566
3
40
12-09 15:30
12-09 23:59
400
8.5
3385
37798
3
40
12-10 0:00
12-10 5:00
400
5
1987
18703
3
40
Total
23.0
9190
96226
Total Week 1
113.0
45856
464366
TABLE 15
ME Pilot Plant Operation Conditions. Week Two
Electrolysis
Current
Time
Current
time
quantity
Power
Circ. Rate
Temp.
From
To
A
h
Ah
Wh
L/min
° C.
Day 6
12-11 23:47
12-12 0:00
400
0.2
85
710
3
40
12-12 0:00
12-12 5:54
400
5.9
2359
20381
3
40
Total
6.1
2444
21091
Day 7
12-12 5:55
12-12 11:58
400
6.0
2422
21166
3
40
12-12 11:58
12-12 23:59
420
12.00
5029
49732
3
40
12-13 0:00
12-13 5:53
420
5.9
2468
26658
3
40
Total
23.9
9920
97556
Day 8
12-13 5:54
12-13 17:55
420
12.0
5036
49160
3
40
12-13 17:56
12-13 23:59
420
6.05
2539
25817
3
40
12-14 0:00
12-14 5:53
420
5.9
2470
24367
3
40
Total
24.0
10044
99344
Day 9
12-14 5:54
12-14 7:58
420
2.1
869
8335
3
40
12-14 8:37
12-14 18:00
420
9.4
3933
38591
3
40
12-14 18:01
12-14 23:59
420
6.0
2502
25998
3
40
12-15 0:00
12-15 5:51
420
5.9
2456
24553
3
40
Total
23.3
9761
97477
Day 10
12-15 5:52
12-15 17:59
420
12.1
5078
42651
3
40-50
12-15 18:00
12-15 19:15
420
1.3
529
4793
3
35
12-15 19:16
12-15 22:14
360-450
3.0
1273
12735
3
35
12-15 22:15
12-15 23:59
420
1.7
733
6854
3
35
12-16 0:00
12-16 5:52
420
5.9
2466
22448
3
35
Total
23.9
10079
89480
Day 11
12-16 5:53
12-16 21:00
420
15.1
6337
61175
3
35
Test t = 35° C.
26.9
11338
108004
Total
15.1
6337
61175
Total Week 2
116.3
48585
466122
During the two 5-day pilot plants about 621 litres of the aqueous composition comprising lithium hydroxide and having a concentration of about 14.6 g/L of lithium (or about 49.9 g/L of lithium hydroxide) and about 2239 litres of the aqueous composition comprising sulphuric acid at a concentration of about 20 to about 30 g/L were produced. A total of about 675.8 litres of the aqueous composition comprising lithium sulphate was processed and about 425 litres of spent electrolyte containing about 2 to about 3 g/L of lithium was produced. Masses, volumes and densities of products produced are provided in Tables 16 and 17. The ME process was conducted for about 228 hours. During the operation about 930.5 kWh of electrical energy was consumed for lithium sulphate conversion to lithium hydroxide.
TABLE 16
ME Pilot Plant Products. Week One
Anolyte
Spent
Catholyte
Feed
Vol-
Vol-
Vol-
Vol-
Mass
ume
Mass
ume
Mass
ume
Mass
ume
Time
kg
L
kg
L
kg
L
kg
L
Initial
60
59.1
60.2
59.5
40
39.5
solution
Day 1
235.8
231.7
70.8
69.6
6.6
6.3
87.3
78.9
Day 2
274.5
269.8
42.84
42.2
80.7
75.9
93.5
84.5
Day 3
270.5
266.0
40.61
40.1
83.0
78.6
88.7
80.2
Day 4
261.2
257.2
35.94
35.5
74.6
70.6
81.4
73.5
Day 5
225.8
222.1
35.10
34.6
65.2
61.6
74.1
66.9
Final
60
59.0
60.2
59.4
53.6
50.6
solution
Total
1267.8
1246.7
225.3
221.9
310.2
315.1
425.0
384.0
Week 1
TABLE 17
ME Pilot Plant Products. Week Two.
Anolyte
Spent
Catholyte
Feed
Vol-
Vol-
Vol-
Vol-
Mass
ume
Mass
ume
Mass
ume
Mass
ume
Time
kg
L
kg
L
kg
L
kg
L
Initial
60
59.0
60.2
59.4
53.5
50.5
solution
Day 6
64.5
63.6
10.3
10.0
13.4
12.7
19.6
17.7
Day 7
238.5
234.6
42.50
41.9
74.9
70.8
76.4
69.1
Day 8
233.4
229.5
45.01
44.3
75.3
71.1
75.3
68.1
Day 9
206.8
203.6
56.67
56.0
56.1
53.1
60.9
55.0
Day 10
165.2
162.7
53.2
52.5
46.2
43.7
54.1
48.9
Day 11
116.6
114.6
35.3
34.9
34.5
32.7
36.6
33.1
Final
43.6
42.9
24.0
23.8
76.0
72.0
solution
Total
1008.6
992.6
206.8
204.0
322.9
305.6
268.9
291.9
Week 2
At the beginning, the starting material aqueous composition in the cathodic compartment contained only about 3.1 g/L Li (about 10.5 g/L of LiOH). During electrolysis the lithium tenor in the catholyte increased. It took about 13 hours for the Li tenor to reach the level of about 15 g/L (about 51.8 g/L of LiOH).
When the Li concentration in the catholyte approached about 15 g/L (about 51.8 g/L of LiOH), reverse osmosis water addition to the cathodic compartment was started. The continuous mode of ME was then started. The Li concentration in the catholyte was maintained by adjusting the dilution water flow to the catholyte reservoir. The Li concentration in catholyte grab samples was about 14 to about 18 g/L during the process (about 48.3 to about 62.1 g/L of LiOH). The Li tenor in the catholyte is plotted against electrolysis time during continuous electrolysis period in the first week of pilot plant operations in
Assay results of selected metals for the profile samples collected from the left and right line of the catholyte stream are listed in Table 18 and Table 19. The catholytes of the left and right compartments were close in composition. The similarity of these values indicated that electrical current was distributed to both cathodes equally and both cells were working with the same effectiveness.
TABLE 18
Assays for catholyte profile samples - Week One.
Tenor, mg/L
Sampling
Li
Na
K
Ca
Mg
time
Left
Right
Left
Right
Left
Right
Left
Right
Left
Right
05Dec 1800
8580
10900
2330
2770
82
101
1.6
1.9
<0.07
<0.07
06Dec 0200
14100
14200
4090
4150
131
115
2.2
2.3
<0.07
<0.07
06Dec 1000
15000
14800
4070
4020
107
107
<0.9
2.1
<0.07
0.08
06Dec 1800
16100
16100
4450
4720
123
128
2.6
2.4
<0.07
<0.07
07Dec 0200
17200
17500
4050
4470
119
119
2.7
2.7
<0.07
<0.07
07Dec 1000
17300
17700
3790
4130
139
137
2.9
2.9
<0.07
<0.07
07Dec 1800
15400
15900
3550
3470
114
123
2.6
2.5
<0.07
<0.07
08Dec 0200
13900
13800
3220
3590
115
114
2.6
2.6
<0.07
<0.07
08Dec 1000
13300
13700
3450
3680
111
115
2.9
3.2
<0.07
<0.07
08Dec 1800
13900
14100
3540
3650
102
104
3.2
3.2
<0.07
<0.07
09Dec 0200
14900
15000
3940
4150
123
117
3.1
3.2
<0.07
<0.07
09Dec 1000
16100
15800
4380
4580
127
118
3.8
3.5
<0.07
<0.07
09Dec 1800
15500
15600
3840
3660
103
101
3.6
3.4
<0.07
<0.07
10Dec 0200
16500
13700
3920
3880
114
117
3.8
3.6
<0.07
<0.07
TABLE 19
Assays for Catholyte Profile Samples - Week Two
Tenor, mg/L
Sampling
Li
Na
K
Ca
Mg
time
Left
Right
Left
Right
Left
Right
Left
Right
Left
Right
12Dec 0200
15300
14900
3410
3360
115
124
3.3
3.7
<0.07
<0.07
12Dec 1000
13900
14400
6110
3820
111
114
3.6
3.7
<0.07
<0.07
12Dec 1800
16100
16500
4240
3690
118
116
4
3.9
<0.07
<0.07
13Dec 0200
16200
16400
3480
3510
114
110
3.5
3.3
<0.07
<0.07
13Dec 1000
14500
14600
3430
3170
118
109
4
3.6
<0.07
<0.07
13Dec 1800
14600
14400
4070
4020
119
157
4.2
3.9
<0.07
<0.07
14Dec 0200
16200
16600
3810
3700
126
129
3.8
3.7
<0.07
<0.07
14Dec 1000
16000
15700
3770
3720
124
135
3.7
4.1
<0.07
<0.07
14Dec 1800
15200
14800
3690
3870
133
134
3.9
3.9
<0.07
<0.07
15Dec 0200
14700
14400
3560
3720
101
109
3.7
3.8
<0.07
<0.07
15 Dec 1000
14400
14300
3870
3980
125
128
3.7
3.8
<0.07
<0.07
15Dec 1800
14800
15300
4040
4240
138
141
3.8
3.9
<0.07
<0.07
16Dec 0200
14700
14700
3870
3860
129
125
3.6
3.4
<0.07
<0.07
16Dec 1000
13900
14000
3900
3880
124
126
3.9
3.8
<0.07
<0.07
16Dec 1800
14000
15600
4120
4270
130
132
4
4
<0.07
<0.07
Lithium hydroxide solution was collected in batches over a 24 h period. The batches were switched out during the Day shift operation. A sample from each drum was taken as day composite sample. Assay results for composite samples are listed in Tables 20 and 21.
The LiOH concentration in product batches starting the second day of pilot plant operation were about 47.3 to about 55.6 g/L (about 14 to about 16 g/L of Li). The obtained aqueous composition also comprised about 3.3 to about 4.5 g/L of Na, about 0.11 to about 0.18 g/L of K and about 2 to about 3.9 ppm Ca. Other impurities were present in non-significant amounts or were below the detection limit of the analytical method.
TABLE 20
Assays for Catholyte Composite Samples: Week One
Sampling
Tenor, mg/L
time
Li
Na
K
Ca
Mg
Ba
Sr
Fe
11Dec-Init
14800
3630
108
3.5
<0.07
0.06
0.56
0.5
12Dec 0600
14500
3260
117
3.9
0.55
0.058
0.63
0.7
13Dec 0600
14600
3640
117
3.7
<0.07
0.047
0.646
<0.2
14 Dec 0600
15500
3560
110
3.8
0.16
0.04
0.61
<0.2
15Dec 0600
14100
3570
129
3.9
<0.07
0.037
0.629
<0.2
16Dec 0600
13700
3640
124
4
<0.07
0.035
0.63
<0.2
16Dec 2100
14200
3550
182
3.7
<0.07
0.02
0.6
<0.2
16Dec Final
16100
3390
119
3.6
<0.07
0.03
0.59
0.2
TABLE 21
Assays for Catholyte Composite Samples: Week Two
Sampling
Tenor, mg/L
time
Li
Na
K
Ca
Mg
Ba
Sr
Fe
11Dec-Init
14800
3630
108
3.5
<0.07
0.06
0.56
0.5
12Dec 0600
14500
3260
117
3.9
0.55
0.058
0.63
0.7
13Dec 0600
14600
3640
117
3.7
<0.07
0.047
0.646
<0.2
14 Dec 0600
15500
3560
110
3.8
0.16
0.04
0.61
<0.2
15Dec 0600
14100
3570
129
3.9
<0.07
0.037
0.629
<0.2
16Dec 0600
13700
3640
124
4
<0.07
0.035
0.63
<0.2
16Dec 2100
14200
3550
182
3.7
<0.07
0.02
0.6
<0.2
16Dec Final
16100
3390
119
3.6
<0.07
0.03
0.59
0.2
At the beginning of pilot plant operation the Li tenor in the spent electrolyte fluctuated between about 1.5 and about 3.5 g/L. The Li tenor was stabilized by adjusting of feed flow rate to the central compartment of the cell. Spent electrolyte collected from the central compartment of the cell at steady state conditions contained about 2.1 to about 2.7 g/L of Li, about 0.36 to about 0.49 g/L of Na and about 8 to about 14 mg/L of K.
The sulphate tenors in anolyte profile samples are plotted in
Data obtained during pilot plant operation were used for calculations of lithium conversion rate, electrical current utilization efficiency, current quantity and power consumption for synthesis of lithium hydroxide. Calculations have been done for each day and week of pilot plant operations as well as for each period of different operation conditions. Calculations were based on amounts of materials produced during the pilot plant campaign and were based on concentration changes in solutions floating in the membrane electrolysis cell. Lithium hydroxide synthesis conditions and calculated parameters are summarized in Tables 22 and 23.
TABLE 22
Lithium Hydroxide and Sulphuric Acid Synthesis Parameters - Week One
Electrolysis
Current
Circ.
Li trans-
Current
Current
time
quantity
Power
Rate
Temp.
Compart-
ferred
effic.
Formed LiOH/H2SO4
Test ID
A
h
A*h
Wh
L/min
° C.
ment
g
%
g
g/h
g/A*h
g/kWh
Day 1
400
19.5
7770
64586
3
40
Cathodic
734
36.5
2532
130
0.33
39.2
Central
1014
50.4
3497
180
0.45
54.2
Anodic
51.7
7353
377
0.95
113.8
Day 2
400-440
23.9
10156
103941
3
40
Cathodic
1241
47.2
4281
179
0.42
41.2
Central
1179
48.1
4068
170
0.40
39.1
Anodic
48.3
8980
375
0.88
86.4
440 A
440
20.1
8809
96629
3
40
Cathodic
1006
44.1
3471
173
0.39
35.9
Central
1078
47.3
3720
185
0.42
38.5
Anodic
45.1
7272
362
0.83
75.3
Day 3
400-440
22.9
9332
103037
3
40
Cathodic
939
38.9
3241
141
0.35
31.5
Central
1167
48.3
4025
176
0.43
39.1
Anodic
43.3
7390
322
0.79
71.7
Day 4
400
23.1
9227
93939
3-6
40
Cathodic
1112
46.5
3836
166
0.42
40.8
Central
1165
41.3
3407
147
0.37
36.3
Anodic
39.6
6681
289
0.72
71.1
6 L/min
400
23.2
9259
84717
6
40
Cathodic
998
41.6
3443
148
0.37
40.6
Central
958
39.9
3305
142
0.36
39.0
Anodic
37.8
6403
276
0.69
75.6
Day 5
400
23.0
9190
96226
6-3
40
Cathodic
868
36.5
2996
130
0.33
31.1
Central
971
40.8
3351
145
0.36
34.8
Anodic
39.1
6581
286
0.72
68.4
Total
400-440
113.0
45856
464366
3-6
40
Cathodic
4894
41.2
16887
149
0.37
36.4
Week 1
Central
5445
45.9
18788
166
0.41
40.5
Anodic
44.0
36893
327
0.80
79.4
The membrane electrolysis stack of two cells equipped with Lanxess Ionac™ membrane, with an effective working area of about 0.84 m2, provided the possibility to produce up to about 179 g of lithium hydroxide per hour. The lithium conversion process performed with a current efficiency of about 43.5% during the first week and at about 34.9% during the second week of pilot plant operation. The average amount of lithium hydroxide produced by per about 1 kWh of electrical energy was about 38.4 g and about 32.5 g for first and second week of pilot plant operation, respectively.
TABLE 23
Lithium Hydroxide and Sulphuric Acid Synthesis Parameters - Week Two
Electrolysis
Current
Circ.
Li trans-
Current
Current
time
quantity
Power
Rate
Temp.
Compart-
ferred
effic.
Formed LiOH/H2SO4
Test ID
A
h
A*h
Wh
L/min
° C.
ment
g
%
g
g/h
g/A*h
g/kWh
Day 6
400
6.1
2444
21091
3
40
Cathodic
228
36.0
787
129
0.32
37.3
Central
293
46.3
1012
166
0.41
48.0
Anodic
40.4
1569
257
0.64
74.4
Day 7
400-420
23.9
9920
97556
3
40
Cathodic
1077
41.9
3716
155
0.37
38.1
Central
1086
42.3
3749
157
0.38
38.4
Anodic
39.6
7186
300
0.72
73.7
Day 8
420
24.0
10044
99344
3
40
Cathodic
1140
43.8
3933
164
0.39
39.6
Central
940
36.1
3243
135
0.32
32.6
Anodic
37.3
6850
286
0.68
69.0
Day 9
420
23.3
9761
97477
3
40
Cathodic
659
26.1
2274
98
0.23
23.3
Central
765
30.3
2639
113
0.27
27.1
Anodic
33.4
5964
256
0.61
61.2
Day 10
360-450
23.9
10079
89480
3
35-50
Cathodic
592
22.7
2044
85
0.20
22.8
Central
598
22.9
2062
86
0.20
23.0
Anodic
25.5
4703
197
0.47
52.6
t = 35° C.
420
26.9
11338
108004
3
35
Cathodic
755
25.7
2605
97
0.23
24.1
Central
803
27.3
2769
103
0.24
25.6
Anodic
34.0
7059
262
0.62
65.4
t = 50° C.
420
6.0
2525
20022
3
50
Cathodic
231
35.4
798
133
0.32
39.8
Central
147
22.5
509
85
0.20
25.4
Anodic
22.4
1035
173
0.41
51.7
Day 11
420
15.1
6337
61175
3
35
Cathodic
856
52.1
2952
195
0.47
48.3
Central
548
33.4
1891
125
0.30
30.9
Anodic
27.0
3134
207
0.49
51.2
Total
400-420
116.3
48585
466122
3
35-50
Cathodic
4544
36.1
15678
135
0.32
33.6
Week 2
Central
4229
33.6
14593
125
0.30
31.3
Anodic
37.0
32933
283
0.68
70.7
It can thus be seen that various parameters have been tested. The person skilled in the art can thus infer that such tests provide a factual basis for making a sound prediction concerning various modifications that can be done to this process and obtaining the same utility. When selecting parameters concerning the temperature, the person skilled in the art will understand that such values can be selected as a function of the tolerance of the membranes and the materials of construction of the ME cell. Tables 24 and 25 provide mass balance for both weeks of tests.
TABLE 24
Mass Balance. Week One.
Materials
Vol
Assays, mg/L
IN
L
Li
Na
K
Ca
Mg
Catholyte Initial
39.5
3100
740
30
<0.9
<0.07
Anolyte Initial
59.1
0.07
<2
<1
<0.9
<0.07
Central Initial
59.5
1880
452
14
<0.9
<0.07
Feed to Central
384.0
15700
3980
107
3.8
0.2
Water to
228.3
0
0
0
0
0
catholyte
Water to anolyte
1314
0
0
0
0
0
OUT
L
Li
Na
K
Ca
Mg
Catholyte Final
53.6
15100
3900
116
3.7
<0.07
Anolyte Final
59.0
0
0
0
0
0
Central Final
59.4
3015
588
12.7
<0.9
<0.07
Product
293.0
14040
3792
124
2.68
<0.07
Anolyte product
1247
0
0
0
0
0
Spent
222
2340
505.7
11.1
<0.9
<0.07
Materials
Mass
Elemental Mass, g
IN
kg
Li
Na
K
Ca
Mg
Catholyte Initial
40.0
122
29.2
1.2
0
0
Anolyte Initial
60.0
0
0
0
0
0.0
Central Initial
60.2
112
27
1
0
0
Feed to Central
425
6029
1528
41
1.5
0.08
Water to
228
0
0
0
0
0
catholyte
Water to anolyte
1314
0
0
0
0
0
OUT
kg
Li
Na
K
Ca
Mg
Catholyte Final
53.6
809
209
6
0.2
0
Anolyte Final
60.0
0
0
0
0
0.0
Central Final
60.2
179
35
1
0
0
Product
310
4208
1144
37
1
0.00
Anolyte product
1268
0
0
0
0
0
Spent
225
515
112
2
0
0
Sum IN
2128
6263
1584
43
2
0
Sum OUT
1977
5712
1500
47
1
0
Accountability %
92.9
91.2
94.7
107.9
67.3
n/a
Distribution (Calculated Head), %
Li
Na
K
Ca
Mg
Catholyte
87.8
90.2
93.1
100
n/a
Spent
12.2
9.8
6.9
0
n/a
Sumcheck
100
100
100
100
n/a
TABLE 25
Mass Balance. Week Two.
Materials
Vol
Assays, mg/L
IN
L
Li
Na
K
Ca
Mg
Catholyte Initial
50.5
14800
3630
108
3.5
<0.07
Anolyte Initial
59.0
446
199
10
<0.9
<0.07
Central Initial
59.4
5180
1500
55
<0.9
<0.07
Feed to Central
291.9
15700
3980
107
3.8
0.2
Water to
284.6
0
0
0
0
0
catholyte
Water to anolyte
986
0
0
0
0
0
OUT
L
Li
Na
K
Ca
Mg
Catholyte Final
72.0
16100
3390
119
3.6
<0.07
Anolyte Final
42.9
0
2
0
0
0
Central Final
23.8
2300
356
8
<0.9
<0.07
Product
284
14433
3537
130
3.8
0.4
Anolyte product
993
0
0
0
0
0
Spent
239.6
2783
517
13
<0.9
<0.07
Materials
Mass
Elemental Mass, g
IN
kg
Li
Na
K
Ca
Mg
Catholyte Initial
53.5
747
183.3
5.5
0.2
0
Anolyte Initial
60.0
26
12
1
0
0
Central Initial
60.2
308
89
3
0
0
Feed to Central
269
4583
1162
31
1.1
0.06
Water to
285
0
0
0
0
0
catholyte
Water to anolyte
986
0
0
0
0
0
OUT
kg
Li
Na
K
Ca
Mg
Catholyte Final
76
1159
244
9
0.3
0
Anolyte Final
43.6
0
0
0
0
0
Central Final
24
55
8
0
0
0
Product
300
4132
1017
36
1.1
0.02
Anolyte product
1009
0
0
0
0
0
Spent
243
606
109
2.6
0
0
Sum IN
1713
5664
1446
40.5
1.3
0.06
Sum OUT
1696
5952
1378
47.2
1.4
0.02
Accountability %
99.0
105.1
95.3
116.3
105.3
31.5
Distribution (Calculated Head), %
Li
Na
K
Ca
Mg
Catholyte
88.9
91.5
94.1
99.2
100
Spent
11.1
8.5
5.9
0.8
0.0
Sumcheck
100
100
100
100
100
In view of the above examples, it can be the the that the contained lithium sulphate in the AR β-spodumene was leached with an efficiency of about 100%. It was observed that a retention time in the range of about 30 to about 45 minutes was sufficient for the CL. It was demonstrated that the CL and PIR circuits can operate without necessarily having a liquid-solid separation step between the two circuits. The lime consumption was about 350 kg dry equivalent mass of lime per about 1000 kg of lithium carbonate equivalent (LCE).
It was also demonstrated that the SIR circuit can be operated in a continuous manner. Impurities such as calcium and magnesium were reduced to levels that can efficiently be processed through ion exchange columns. The consumption of NaOH was about 10 kg per about 1000 kg LCE. It was determined that calcium continued to precipitate from solution after this solution had left the SIR circuit. In one such example the calcium tenor in the SIR 4 reactor was about 286 mg/L. The filtrate of this solution on sitting for several hours had a calcium tenor of about 140 mg/L. The SIR product slurry was approximately about 0.4% solids by weight. These solids had a Li content of about 4.4% and accounted for about 0.5% of the total Li processed.
The processes were effective for reducing the calcium and magnesium tenors in the lithium sulphate solution to below about 10 mg/L.
The processes were effective for removing about 97.6% of the contained calcium and about 99.0% of the contained magnesium from the lithium sulphate solution. Therefore, a high purity and high quality lithium sulphate was produced. Only about 2.7% of the lithium was removed by the processes.
The processes involving the electrolysis carried out by membrane electrolysis in the three-compartment cell was effective for converting lithium sulphate to lithium hydroxide. It was demonstrated that the lithium hydroxide production from lithium sulphate could operate in a continuous manner using a three-compartment membrane electrolysis cell. The aqueous composition comprising lithium hydroxide was produced in the cathodic compartment, sulphuric acid was formed in the anodic compartment and a composition having a low tenor in lithium sulphate overflowed from the central compartment. The pilot plant produced about 621 litres of an aqueous composition comprising lithium hydroxide having a concentration of about 14.6 g/L of lithium (about 50.4 g/L of lithium hydroxide) and about 2239 litres of sulphuric acid having a concentration of about 20 to 30 g/L. The lithium hydroxide that was produced was of a good quality. The aqueous composition comprising lithium hydroxide solution contained about 3.7 g/L of sodium and about 121 mg/L of potassium. The trace impurities present at levels of less than about 10 mg/L in the lithium hydroxide were Ba, Ca, Cr, Cu, Fe, Mg, Mn and Sr.
Alternate Process Using Ammonia to Neutralize Acid.
Applicant has previously shown in U.S. 61/788,292 (hereby incorporated by reference in its entirety) that lithium hydroxide can be successfully recovered at high efficiencies from a lithium sulfate process stream at temperatures of about 40° C. or about 60° C., using electrolysis with a Nafion 324 cation exchange membrane and either an Asahi AAV or a Fumatech FAB anion exchange membrane. In both cases, sulfuric acid was produced as a coproduct. An alternate process where ammonium sulfate is produced instead of sulfuric acid may be useful and the present disclosure details work demonstrating its feasibility. Tests were performed using a similar electrolysis cell as in U.S. 61/788,292, except that the highly resistive proton-blocking Fumatech™ FAB membrane was replaced with a Neosepta™ AHA membrane. The AHA membrane is an anion membrane manufactured by Astom™ (Japan) with a higher temperature stability (about 80° C.) and is expected to, for example have good electrical resistance for sulfate transport.
Current efficiency for hydroxide production (about 80% at about 3 M) matched the highest obtained in the previous studies when the feed was kept at an about neutral pH. Salt production at very high efficiency was initially possible. However, as the batch proceeded the hydroxide inefficiency (about 20%) caused an increase in the feed pH and the hydroxide in the feed competed with sulfate transport across the AHA membrane.
Based on the testing performed in the present studies, a continuous process using Nafion 324 and AHA membranes at about 60° C. would be expected to have the following characteristics, and is compared with results for the known Sulfuric Acid Process in Table 26 below.
TABLE 26
Comparison of Sulfuric Acid and Ammonium Sulfate Processes
Sulfuric Acid Process
Ammonium Sulfate Process
Recommended Process
Batch
Continuous
Membranes
N324/FAB
N324/AHA
Sulfuric Acid/Ammonium Sulfate
0.75M
3M
Lithium Hydroxide
3-3.2M
3-3.2M
Average Current Density
100 mA/cm2
550 mA/cm2
Current Efficiency for Hydroxide
75%
80%
Cell Voltage in Custom Cell
6 V
4.6 V
Water Transport: Feed to Base
8 mol water per mol cation
8 mol water per mol cation
Water Transport: Feed to Acid
<1 mol water per mol cation
12 mol water per mol cation
Previous studies (U.S. 61/788,292) have shown that lithium hydroxide can be successfully recovered at high efficiencies from a lithium sulfate process stream at temperatures of about 40° C. or about 60° C., using electrolysis with a Nafion 324 cation exchange membrane and either an Asahi AAV or a Fumatech FAB anion exchange membrane. In both cases, sulfuric acid was produced as a coproduct. The production of sulfuric acid can limit, for example the choice of anion membrane in the system, the acid concentration which can be achieved and the temperature of operation.
Certain anion exchange membranes such as a proton-blocking membrane which has a high resistance especially for sulfate transport such as the Fumatech FAB membrane or a similar membrane, may, for example limit the current density achieved in a process for preparing lithium hydroxide. However, these membranes can be limited to a temperature of about 60° C.
Highly concentrated ammonium sulfate (>about 2 M) can be produced in a similar electrolysis cell, and due, for example to the buffering capacity of bisulfate and the ability to dissolve ammonia in solution, it is possible to make the anolyte solution non-acidic as shown in
Such a process may, for example remove the higher resistance FAB membrane possibly allowing operation at either higher current density (thereby reducing membrane area), lower voltage (thereby reducing power consumption) or a combination of the two. It may also, for example, generate an alternate commercial material. Ammonium sulfate can be sold as an ingredient for fertilizer and should have a higher value than the sulfuric acid. It is also, for example expected to remove more water during the electrolysis from the feed thereby allowing more efficient operation over a wider range of feed conversion. It may also, for example, allow operation of the process at a higher temperature requiring less cooling of solutions. Solutions and membranes are also less resistive at these higher temperatures decreasing power consumption.
The tests performed on this system, where the anion membrane used in the previous process (Fumatech FAB) is replaced by a Neosepata AHA (Astom Corp.) membrane and ammonia is used to control the pH of the “acid” compartment of the cell are summarized below.
The experiments were carried out in an Electrocell MP cell similarly equipped to that used in the previous studies (U.S. 61/788,292) but wherein the anion membrane was replaced with a Neosepta AHA (Astom Corp.) membrane.
The various electrolyte circuits were similar to those used in the previous studies (U.S. 61/788,292), except that pH control was added to the anolyte (acid/salt) circuit. The pH controller actuated a solenoid valve which allowed addition of ammonia gas directly to the anolyte reservoir. Care was taken to not allow the anolyte pH to increase above about 5 as the DSA-O2 coating can be removed at high pH. In addition to those analyses previously performed, ammonium ion was analyzed by cation ion chromatography. All other aspects of the experimental setup were the same as described previously.
During the course of the present studies, experiments of varying duration were performed. These experiments evaluated the effect of temperature, current density, feed conversion, acid/salt concentration, base concentration and pH control strategy on current efficiencies, voltage and water transport. Concentration ranges and current efficiencies are summarized in Table 27. In the first two experiments, the concentration of base and acid/salt were allowed to increase from their starting values. The second experiment ran over two days to provide a greater amount of sulfate removal. In this case, due to volume limitations of the setup, water had to be added to the feed to obtain more than about 90% removal. In the remaining experiments water was only added to the acid and base compartments in an effort to maintain about constant salt and base concentrations (simulating continuous production). Experiments 856-81 through 856-86 were run under about constant acid (about 2.5-3 M sulfate) and base (about 2.8-3.1 M hydroxide) to probe the effect of varying temperature and current density. The final two experiments varied the control pH of the acid compartment in an effort to mediate problems with the resulting feed pH.
TABLE 27
Summary of Results for Ammonium Sulfate Production. Sulfate current
efficiency (CE) reported for each of the product streams.
FEED
ACID
SO42−
%
SO42−
BASE
Experiment
Conditions
[SO42−]/M
CE3
REMOVAL
[SO42−]/M
CE
[OH−]/M
OH− CE
856-71
150 mA/cm2,
1.60-1.06
94%
61%
1.00-1.26
93%
1.43-2.97
76%
60° C., no water
856-78
150 mA/cm2,
1.74-0.18
84%
95%
2.69-3.37
77%
2.34-3.38
77%
60° C., water to
base and feed
856-81
150 mA/cm2,
1.77-0.78
91%
80%
2.95-2.74
88%
2.97-2.79
79%
60° C., water to
base and acid
856-84
200 mA/cm2,
1.56-0.67
80%
83%
2.47-2.38
88%
2.79-3.08
83%
60° C., water to
base and acid
856-86
200 mA/cm2,
1.67-0.63
83%
86%
2.39-2.63
88%
3.08-2.97
80%
80° C., water to
base and acid
856-88
200 mA/cm2,
1.73-0.82
83%
78%
2.53-2.70
87%
2.97-3.20
80%
60° C., lower
acid pH
856-90
cont. 856-88
1.73-0.75
72%
81%
2.70-3.72
75%
3.20-3.49
73%
with new feed
Typically the sulfate current efficiency in the feed should equal the sulfate current efficiency in the acid. As shown in Table 27, there is a discrepancy of up to about 8% in some of the experiments. While not wishing to be limited by theory, the majority of this error is likely due to volume measurement error due to hold in the setup, for example when dealing with solutions of high concentration.
Lithium Hydroxide Production
The process produced lithium hydroxide at hydroxide concentrations of about 3 M. The efficiency was fairly consistent throughout the testing, giving numbers slightly below about 80% at about 150 mA/cm2, increasing to over about 80% at the higher current density. In the last experiment, the lithium hydroxide concentration was allowed to increase to about 3.5 M and the current efficiency decreased by about 7%. In these experiments, the efficiency is predominantly hydroxide back migration as, unlike the previous studies, the pH of the feed was always greater than about 7 eliminating any proton transport. However, there may also be some inefficiency associated with ammonium transport. As shown in
Ammonium Sulfate Production
In the majority of the experiments, the ammonium sulfate concentration was kept at about 2.5 to about 3 M sulfate as shown in
Lithium Sulfate Feed Depletion
In the majority of the experiments (except 856-78), no water was added to the feed. Due to limitations of the setup (and time required for larger batches), most experiments were stopped after about 80% conversion. With the amount of water transport, the lithium sulfate concentration was still high at the end of the test as shown in
Experimental Trial at Lower Acid pH (Anolyte pH)
For example, in some experiments of the present studies, the feed pH was allowed to increase due to the hydroxide back migration in the feed. One control method that could be used to circumvent this issue is to add sulfuric acid into the feed to maintain its pH between about 7 and 10. Since the hydroxide production efficiency is about 80%, acid equaling about 20% of the charge would be required.
Alternatively, the pH setpoint on the acid/salt could be modified to allow for some proton back migration. In this case, if the feed pH is above a certain measured setpoint (for example about 9.5, about 9.7 or about 10), then the ammonia addition to the acid is stopped. The pH on the acid drops allowing for proton back migration until the feed pH decreases below the required setpoint. Ammonia is then added to the acid to increase the pH and the process is repeated. The above method allows for self-correction of the process and does not require any external sulfuric acid. It will be appreciated that pH measurement in solutions of high concentration salt may be inaccurate, as the sodium (and lithium) ions may, for example interfere with the measured pH. Typically the measured pH can be a couple of pH units different than the actual pH; typically lower in alkaline salt solutions and higher in acid. It will be appreciated that care must be taken to calibrate and offset for this effect, for example when using pH as a control algorithm. Graphs shown in the present disclosure are as measured.
The last two experiments used this type of control. 856-88 started with about 2.5 M ammonium sulfate at a pH of about 3.5 and was allowed to run without any further ammonia addition. As shown in
The final experiment, 856-90, was a continuation of the previous experiment, except that new feed solution was used. As shown in
The present tests demonstrated that it is possible to run the process in this way. The current efficiencies for hydroxide production, feed sulfate removal and acid sulfate production (as shown in Table 27) were more closely balanced. However, the caustic strength was slightly higher for this run, making the overall current efficiency closer to about 73%.
The concentration of ammonium in the salt running at a measured pH of about zero is about half the concentration of the same sulfate concentration solution running at a pH of about 3.5 (i.e. NH4HSO4 instead of (NH4)2SO4) which would decrease the amount of ammonium back migration and therefore the amount of ammonium transport into the base.
Cell Voltage and Water Transport
An advantage of the ammonium sulfate system over the sulfuric acid system was the potentially higher current density and lower cell voltage that could be obtained when the highly resistive Fumatech FAB membrane was removed from the process.
Table 28 shows the cell voltage ranges obtained for the current work, requiring about 6 V at about 150 mA/cm2 and about 6.5 V at about 200 mA/cm2. In previous work, a constant cell voltage of about 7.8 V was used to obtain an average current density of about 100 mA/cm2. Therefore higher current densities have been obtained at lower voltages a cell with about 2 mm solution gaps run as low as about 4.6 V at about 60° C. It will be appreciated that there is less change from the Prodcell to the commercial cell since the feed can be run at higher conductivity. Running the cell at about 80° C. decreased the cell voltage by about 0.6 V when running at about 200 mA/cm2. However, this impact may be less in the commercial cells as the main improvement is in solution conductivity and the commercial cell has smaller solution gaps.
TABLE 28
Cell Voltage Range and Water Transport Numbers.
Water Transport (mol H2O/mol Q)5
Experiment
Conditions
Voltage/V
Feed
Acid
Base
856-71
150 mA/cm2, 60° C., no
6.4-5.5
9.3
4.4
4.7
water addition
856-78
150 mA/cm2, 60° C., water
5.6-6.3
10.9
4.4
6.2
addition to base and feed
856-81
150 mA/cm2, 60° C., water
5.9-5.8
9.6
8.8
5.9
addition to base and acid
856-84
200 mA/cm2, 60° C., water
6.8-6.4
10.7
5.9
7.5
addition to base and acid
856-86
200 mA/cm2, 80° C., water
6.0-5.7
10.2
3.8
6.5
addition to base and acid
856-88
200 mA/cm2, 60° C., lower
6.0-6.3
9.0
4.6
6.3
acid pH
856-90
cont. 856-88 with new
6.5-6.8
8
2.4
7.7
feed
Water transport in this system was fairly high, averaging about 10 mol of water transport per mol of charge (about 22 mol water per mol of lithium sulfate transport). This is about half the water required in order to maintain a constant feed concentration and therefore allow the system to run in a completely continuous process. It may be possible to incorporate a reverse osmosis unit on the feed stream to remove the remaining water, thereby allowing full conversion of the feed. The experiments running at lower acid pH had lower associated water transport. While not wishing to be limited by theory, this effect is likely due to some water transport associated with proton back migration and lower osmotic drag into the acid. Although the sulfate concentration was about the same in the two solutions, there was much less ammonium in the last two experiments.
The water transport numbers are quoted per mole of charge. Per mole of cation in the base, these numbers need to be divided by the current efficiency. Per mole of sulfate into the acid, these numbers need to be multiplied by two and divided by the current efficiency.
Based on the testing performed in the present studies, the process may, for example produce ammonium sulfate at a concentration of about 3 M or higher if lower pH control was used, produce lithium hydroxide at a concentration of about 3 M, have an average current density of about 150 mA/cm2, have a current efficiency of about 80% for hydroxide production, have a cell voltage of about 4.6 V for a custom-designed cell, have water transport from feed to base of about 8 mol water per mol cation and have water transport from feed to acid/salt of about 12 mol water per mol sulfate or less if a lower pH on acid is used, for example.
When compared to the previous sulfuric acid process, these conditions may, for example decrease the required cell area for a plant producing about 3 tonne/hour of LiOH, by over about 35%. It may also, for example decrease the power consumption for a commercially designed cell from about 8.9 kWh/kg of LiOH to about 6.4 kWh/kg of LiOH (in an about 3 M solution). It also may, for example produce between about 8-10 tonne/hour of ammonium sulfate (dry basis) depending on the feed pH control regime.
Hydroxide back migration across the N324 membrane increases the pH of the feed. This transport may affect the overall process and different control strategies may be used to provide steady operation. Three different control strategies may, for example be used:
For example sulfuric acid may be used to control the feed pH around a neutral to slightly basic pH (about 7-9). This method, for example require an additional control circuit and may, for example require purchase of sulfuric acid. The additional sulfuric acid purchased is converted into ammonium sulfate. Lithium hydroxide production may still be at about 80% current efficiency and ammonium sulfate may be between about 90%-100%. An inefficiency may be ammonium back-migration across the AHA. This option may be useful if, for example a suitable sulfuric acid source, and an outlet for the ammonium sulfate produced exists.
For example, no remediation may be performed and the feed pH may increase until the inefficiency of hydroxide across the AHA matches that of hydroxide across the N324. This may, for example make both lithium hydroxide and ammonium sulfate efficiencies the same. Although it may be the easiest to implement, the stability of the anion exchange membrane in high pH solution and temperature may, for example need to be considered. For example, a base stable anion exchange membrane may be used.
For example, variation in the pH of the ammonium sulfate may be allowed so that some proton back-migration is allowed. If the feed pH increases the amount of ammonia added to the acid/salt is stopped, proton is produced at the anode until enough proton has migrated across the AHA to bring the feed pH lower, and then ammonia addition occurs again. This method again matches lithium hydroxide and ammonium sulfate production, but may keep the pH at the AHA low. It also, for example has a benefit of running the acid/salt with a lower ammonium concentration. For example, an about 3 M sulfate solution might comprise about 0.5 M sulfuric acid with about 2.5 M ammonium bisulfate at a pH of about zero, but may comprise almost about 6 M ammonium sulfate at pH of about 4. This may, for example decrease the amount of ammonium back migration on the AHA membrane. The acid/salt solution could then, for example be post neutralized with ammonia to produce the required about 3 M (NH4)2SO4 solution. Higher sulfate concentrations could also, for example be used.
While a description was made with particular reference to the specific embodiments, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as specific examples and not in a limiting sense.
Bourassa, Guy, Pearse, Gary, Mackie, Stephen Charles, Gladkovas, Mykolas, Magnan, Jean-François, Symons, Peter, Genders, J. David
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